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Understanding Your Thyroid Test Results

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Science Based

Written by  Amy Myers, MD

Your thyroid is a complex organ that wears many hats. Because of this, I often get asked a lot of questions. Some of the most frequent questions I get is, “How do I interpret my thyroid test results, and which tests are most important?” These are important questions to ask, and let me tell you, there is a lot of misinformation out there. Both the internet and conventional medicine world have a lot of misinformation surrounding thyroid tests, thyroid test results, and thyroid medication. That’s why I discuss them in-depth in my book, “ The Thyroid Connection .”

I’ll explain the different types of thyroid tests, as well as how to interpret your thyroid test results. Also, I’ll go over why your doctor should carefully review your thyroid test results. This is important, because what may be “normal” is not necessarily optimal. There are optimal reference ranges for thyroid test results you can aim for. This can help you and your doctor ensure you enjoy the benefits of optimal thyroid levels.

Types of Thyroid Hormone Tests & Optimal Thyroid Levels

Many doctors who suspect a thyroid disorder start by checking Thyroid Stimulating Hormone (TSH) test levels. TSH tests usually reveal whether someone is dealing with hyperthyroidism vs hypothyroidism.  TSH acts like an “early warning sign” and will usually give a clue that something could be heading in the wrong direction. 

If they’re lucky, a doctor might test a person’s Free T4 levels. Free T4 shows if there’s a shortage of the storage form of thyroid hormones. While these thyroid test results do a great job to uncover the nature of a patient’s disease, they only tell you a small part of the story.

Other thyroid tests include T3 tests, Free T3, and Reverse T3. There are also thyroid antibody tests. To get a complete picture of a patient’s thyroid health and medical needs, I recommend working with a doctor who orders all six blood tests listed below.

Thyroid Stimulating Hormone (TSH)

The hypothalamus is the control center of your brain. It is responsible for managing many body functions. For example, hunger, thirst, sleep, hormones, and body temperature, among other processes. The hypothalamus also continuously monitors the level of thyroid hormones present in your bloodstream. 1 If it determines that energy levels are low, it sends out TRH, or Thyroid Releasing Hormone, to your pituitary gland.

Your pituitary gland receives the TRH and responds by releasing TSH, or Thyroid Stimulating Hormone. TSH goes directly to your thyroid to produce more thyroxine, or T4. Your TSH level is an indication of what your pituitary gland is doing. We know this based on your hypothalamus’ feedback loop. The problem is that it’s not actually an indicator on how your thyroid is actually functioning. As a result, there is a misunderstanding of thyroid test results. This often leads to counterintuitive patient advice.

TSH Thyroid Test Results

• If your TSH test level is high in your thyroid test results, this can be a sign that you are under-producing thyroid hormones and you are hypothyroid.
• If your TSH test level is low in your thyroid test results, this can be a sign that you are over-producing thyroid hormones and are hyperthyroid. Or, it could also mean you are on too much supplemental thyroid hormone. Supplemental T3, or natural desiccated thyroid hormone with T3, can artificially suppress your TSH levels. So, in the absence of symptoms, it could be perfectly fine if the level appears low.

Normal vs Optimal Thyroid Levels

If your thyroid test results show “normal” TSH test levels, you may not have a thyroid dysfunction. By “normal”, I mean it falls within the normal reference range used by most conventional doctors. However, as I write in my book , “normal” and “optimal” levels mean very different things. If you still have symptoms yet fall within the “normal” range for thyroid test results, you may still have thyroid dysfunction. One example of this includes subclinical hypothyroidism. 2

What is T4, or the Storage Form of Thyroid Hormone?

Once TSH signals your thyroid to ramp up hormone production, it produces several different types of thyroid hormone. For example, your thyroid releases T1, T2, T3, and T4. It also releases calcitonin, which helps regulate calcium. The primary output of your thyroid is T4, which is a storage form of the hormone. It circulates throughout the bloodstream and stays in the tissues. That way, it’s available when needed. I like to measure Free T4 (FT4) since it is unbound and able to act in the body.

Free T4 Thyroid Test Result

• If your Free T4 level is high in your thyroid test results, it can mean an overactive thyroid or hyperthyroidism. 
• If your Free T4 is low in your thyroid test results, it can mean an under-active thyroid or central hypothyroidism.

What is Free T3, or “the Gas”?

When each local area of your body determines that it needs more power, it converts storage T4 and Free T3. While T4 is the storage form of thyroid hormone, T3 is the active form of the hormone. These hormones attach to receptors inside of your cells to power your metabolic processes. This is why I like to think of them as the gas. 3

Free T3 Thyroid Test Result

• If your Free T3 level is high in your thyroid test results, it indicates that your thyroid is overactive or hyperthyroidism.
• If your Free T3 is low in your thyroid test results, you may not be converting T4 to Free T3 very well. You could have hypothyroid symptoms, even if your TSH level and Free T4 level are within the “normal” range in thyroid test results. This is one of the most common causes of low thyroid or hypothyroidism that I saw in my clinic.

What is Reverse T3, or “the Brakes”?

Your body also uses some of the T4 to create Reverse T3 (RT3). Reverse T3 is another inactive form of thyroid hormone. This one can attach to the receptors for Free T3 to slow down your metabolic processes. For that reason, I call RT3 the brakes. 4

Reverse T3 Thyroid Test Result

• If RT3 is high – you are likely converting too much T4 to RT3 and not enough to FT3. This can cause hypothyroid symptoms, even if your TSH and T4 levels are optimal. 
• Also, I look at something called an RT3:FT3 ratio. I like that to be less than a 10:1 ratio.

What are Thyroid Antibodies?

The vast majority of thyroid conditions are autoimmune. Autoimmune conditions happen when your immune system attacks itself. In this case, your immune system attacks your thyroid. The hypothyroid form of autoimmune thyroid disorder is Hashimoto’s. On the flip side, the hyperthyroid form (which is what I had) is Graves’ disease. It’s incredibly important to know if your thyroid condition is autoimmune . After all, once you develop one autoimmune disease, you’re more likely to develop another.

There’s another reason this is important. As I explain in both of my books, The Thyroid Connection , and The Autoimmune Solution , addressing the root cause can help reverse autoimmune disease. Some of the biggest causes include leaky gut , diet, toxins , infections, and stress .

There are two main types of thyroid antibodies. The first type is thyroid peroxidase antibodies (TPOAb). These attack an enzyme used to synthesize thyroid hormones. TPOAb are commonly elevated in both Hashimoto’s and Graves’ disease patients. Thyroglobulin Antibodies (TgAb), attack thyroglobulin, which your thyroid uses to produce its hormones. These thyroid antibodies are typically elevated in Hashimoto’s patients.

Thyroid Antibodies Test Result

• If your antibodies are high, your immune system is attacking your thyroid. This could mean one of two outcomes. Either you have autoimmune thyroid disease, or you are on the Autoimmune Spectrum® .

What Thyroid Tests Should Your Doctor Order?

Most conventional medicine doctors only check your Thyroid Stimulating Hormone (TSH) levels and Free T4 levels to see if you are low on the storage form of thyroid hormones. However, as we’ve just covered, optimal thyroid function involves many factors. Those two levels of thyroid test results alone don’t tell the whole story. I recommend ordering the following tests to get a complete picture of a patient’s thyroid problems and health.

• Free T4 
• Free T3 
• Reverse T3 
• Thyroid Peroxidase Antibodies (TPOAb)
• Thyroglobulin Antibodies (TgAb)

The Optimal Thyroid Levels

Even if your doctor does order a complete thyroid function test panel, they’re usually relying on “normal” thyroid test results reference ranges that are too broad and often inaccurate. When lab reference ranges for a healthy thyroid were created, it was later discovered that people who already had thyroid dysfunction were included in those ranges! 

Because of this, in 2003, the American Association of Clinical Endocrinologists recommended that the lab reference ranges for thyroid test results become more narrow. Yet still today, most doctors and laboratories haven’t updated their practices for optimal thyroid levels.

In my clinic, I found that the ranges below are where my patients (and myself) thrived, not just lived! I listened to my patients and took how they were feeling into account as well. 5

  I believe the most optimal thyroid levels are:

• TSH levels of 1-2 UIU/ML or lower (Armour or compounded T3 can artificially suppress TSH)
• FT4  levels >1.1 NG/DL
• FT3 levels > 3.2 PG/ML
• RT3 levels < 10:1 ratio RT3:FT3
• TPO – TgAb levels < 4 IU/ML or negative

If Your Doctor Won’t Order a Full Thyroid Panel for You

My sincere hope is that your doctor is willing to order all of the labs listed above and then use the optimal thyroid levels reference ranges while working with you to restore your optimal thyroid levels. However, if that is not the case, I recommend using a lab company such as My Labs for Life so that you can easily order a complete thyroid panel and take your results back to your physician to have them reviewed.

The Myers Way® to Support Thyroid Health

The Myers Way® Multivitamin is tailor-made to help support optimal thyroid levels. I personally lived with thyroid issues. I’ve spent my career perfecting the art of supporting thyroid health for myself, the patients in my clinic, and, now, anyone who wants to support healthy thyroid and adrenal function. I custom-formulated this multi to be the perfect multivitamin for virtually everyone. However, I created it for those with thyroid dysfunction in mind. In fact, all of my patients with hypo- or hyperthyroidism, including Hashimoto’s and Graves’ disease, had my daily multivitamin in their treatment plans.

This specially-formulated multi is jam-packed with micronutrients in the forms your body wants and the amounts your thyroid needs. With optimal levels of thyroid-supporting minerals such as zinc, selenium, and iodine, alongside antioxidants including vitamins C and E and other free radical scavengers, no other multivitamin on the market does more to support your thyroid!

Article Sources

• Physiology of the Hypothalamic-Pituitary-Thyroid Axis . Stefano Mariotti, Paolo Beck-Peccoz. NCBI. 2016.
• High and low TSH Levels: What They Mean . Mary Shomon. Very Well Health. 2019.
• What to Know About T3 Levels . Aaron Kandola. Medical News Today. 2020.
• Overview of Reverse T3 Thyroid Hormone . Mary Shomon. Very Well Health . 2020.
• Interpreting Thyroid Levels Tests . Corey Whelan. Healthline. 2019.

The Myers Way® Multivitamin

Amy Myers,  MD

Amy Myers, MD is a two-time New York Times bestselling author and an internationally acclaimed functional medicine physician. Dr. Myers specializes in empowering those with autoimmune, thyroid, and digestive issues to reverse their conditions and take back their health. In addition, she is a wife, mother, and the successful  founder and CEO of  Amy Myers MD ® .

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Home » Thyroid Function Tests

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Thyroid Function Tests

What is the thyroid gland.

The thyroid gland is a butterfly-shaped endocrine gland that is normally located in the lower front of the neck. The thyroid’s job is to make thyroid hormones, which are secreted into the blood and then carried to every tissue in the body. Thyroid hormones help the body use energy, stay warm and keep the brain, heart, muscles, and other organs working as they should.

HOW DOES THE THYROID GLAND FUNCTION?

The major thyroid hormone secreted by the thyroid gland is thyroxine, also called T4 because it contains four iodine atoms. To exert its effects, T4 is converted to triiodothyronine (T3) by the removal of an iodine atom. This occurs mainly in the liver and in certain tissues where T3 acts, such as in the brain. The amount of T4 produced by the thyroid gland is controlled by another hormone, which is made in the pituitary gland located at the base of the brain, called thyroid stimulating hormone (abbreviated TSH). The amount of TSH that the pituitary sends into the bloodstream depends on the amount of T4 that the pituitary sees. If the pituitary sees very little T4, then it produces more TSH to tell the thyroid gland to produce more T4. Once the T4 in the bloodstream goes above a certain level, the pituitary’s production of TSH is shut off. In fact, the thyroid and pituitary act in many ways like a heater and a thermostat. When the heater is off and it becomes cold, the thermostat reads the temperature and turns on the heater. When the heat rises to an appropriate level, the thermostat senses this and turns off the heater. Thus, the thyroid and the pituitary, like a heater and thermostat, turn on and off. This is illustrated in the figure below.

T4 and T3 circulate almost entirely bound to specific transport proteins. If the levels of these transport proteins changes, there can be changes in how much bound T4 and T3 is measured. This frequently happens during pregnancy and with the use of birth control pills. The “free” T4 or T3 is the hormone that is unbound and able to enter and affect the body tissues.

Blood tests to measure these hormones are readily available and widely used, but not all are useful in all situations. Tests to evaluate thyroid function include the following:

TSH TESTS The best way to initially test thyroid function is to measure the TSH level in a blood sample. Changes in TSH can serve as an “early warning system” – often occurring before the actual level of thyroid hormones in the body becomes too high or too low. A high TSH level indicates that the thyroid gland is not making enough thyroid hormone (primary hypothyroidism). The opposite situation, in which the TSH level is low, usually indicates that the thyroid is producing too much thyroid hormone (hyperthyroidism). Occasionally, a low TSH may result from an abnormality in the pituitary gland, which prevents it from making enough TSH to stimulate the thyroid (secondary hypothyroidism). In most healthy individuals, a normal TSH value means that the thyroid is functioning properly.

T4 TESTS T4 is the main form of thyroid hormone circulating in the blood. A Total T4 measures the bound and free hormone and can change when binding proteins differ (see above). A Free T4 measures what is not bound and able to enter and affect the body tissues. Tests measuring free T4 – either a free T4 (FT4) or free T4 index (FTI) – more accurately reflect how the thyroid gland is functioning when checked with a TSH.

The finding of an elevated TSH and low FT4 or FTI indicates primary hypothyroidism due to disease in the thyroid gland. A low TSH and low FT4 or FTI indicates hypothyroidism due to a problem involving the pituitary gland. A low TSH with an elevated FT4 or FTI is found in individuals who have hyperthyroidism .

T3 TESTS T3 tests are often useful to diagnosis hyperthyroidism or to determine the severity of the hyperthyroidism. Patients who are hyperthyroid will have an elevated T3 level. In some individuals with a low TSH, only the T3 is elevated and the FT4 or FTI is normal. T3 testing rarely is helpful in the hypothyroid patient, since it is the last test to become abnormal. Patients can be severely hypothyroid with a high TSH and low FT4 or FTI, but have a normal T3.

FREE T3 Measurement of free T3 is possible, but is often not reliable and therefore not typically helpful.

REVERSE T3 Reverse T3 is a biologically inactive protein that is structurally very similar to T3, but the iodine atoms are placed in different locations, which makes it inactive. Some reverse T3 is produced normally in the body, but is then rapidly degraded. In healthy, non-hospitalized people, measurement of reverse T3 does not help determine whether hypothyroidism exists or not, and is not clinically useful.

THYROID ANTIBODY TESTS

The immune system of the body normally protects us from foreign invaders such as bacteria and viruses by destroying these invaders with substances called antibodies produced by blood cells known as lymphocytes. In many patients with hypothyroidism or hyperthyroidism, lymphocytes react against the thyroid (thyroid autoimmunity) and make antibodies against thyroid cell proteins. Two common antibodies are thyroid peroxidase antibody and thyroglobulin antibody. Measuring levels of thyroid antibodies may help diagnose the cause of the thyroid problem. For example, positive anti-thyroid peroxidase and/or anti-thyroglobulin antibodies in a patient with hypothyroidism result in a diagnosis of Hashimoto’s thyroiditis. While detecting antibodies is helpful in the initial diagnosis of hypothyroidism due to autoimmune thyroiditis, following their levels over time is not helpful in detecting the development of hypothyroidism or response to therapy. TSH and FT4 are what tell us about the actual thyroid function or levels.

A different antibody that may be positive in a patient with hyperthyroidism is the stimulatory TSH receptor antibody (TSI). This antibody causes the thyroid to be overactive in Graves’ Disease . If you have Graves’ disease, your doctor might also order a thyrotropin receptor antibody test (TSHR or TRAb), which detects both stimulating and blocking antibodies. Following antibody levels in Graves’ patients may help to assess response to treatment of hyperthyroidism, to determine when it is appropriate to discontinue antithyroid medication, and to assess the risk of passing antibodies to the fetus during pregnancy.

THYROGLOBULIN Thyroglobulin (Tg) is a protein produced by normal thyroid cells and thyroid cancer cells. It is not a measure of thyroid function and it does not diagnose thyroid cancer when the thyroid gland is still present. It is used most often in patients who have had surgery for thyroid cancer in order to monitor them after treatment. Tg is included in this brochure of thyroid function tests to communicate that, although measured frequently in certain scenarios and individuals, Tg is not a primary measure of thyroid hormone function.

NON-BLOOD TESTS

RADIOACTIVE IODINE UPTAKE Because T4 contains iodine, the thyroid gland must pull a large amount of iodine from the bloodstream in order to make an appropriate amount of T4. The thyroid has developed a very active mechanism for doing this. Therefore, this activity can be measured by having an individual swallow a small amount of iodine, which is radioactive. The radioactivity allows the doctor to track where the iodine goes. By measuring the amount of radioactivity that is taken up by the thyroid gland (radioactive iodine uptake, RAIU), doctors may determine whether the gland is functioning normally. A very high RAIU is seen in individuals whose thyroid gland is overactive ( hyperthyroidism ), while a low RAIU is seen when the thyroid gland is underactive ( hypothyroidism ). In addition to the radioactive iodine uptake, a thyroid scan may be obtained, which shows a picture of the thyroid gland and reveals what parts of the thyroid have taken up the iodine (see Thyroid Nodules brochure ).

MEDICATIONS THAT INTERFERE WITH THYROID FUNCTION TESTING

There are many medications that can affect thyroid function testing. Some common examples include:

• Estrogens , such as in birth control pills, or in pregnancy, cause high levels of total T4 and T3. This is because estrogens increase the level of the binding proteins. In these situations, it is better to ask both for TSH and free T4 for thyroid evaluation, which will typically be in the normal range.
• Biotin , a commonly taken over-the-counter supplement, can cause the measurement of several thyroid function tests to appear abnormal, when they are in fact normal in the blood. Biotin should not be taken for 2 days before blood is drawn for thyroid function testing to avoid this effect.

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Thyroid function tests

Revised 2021

Your guide to thyroid function tests

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Also available in  Arabic, Polish and Urdu and Mandarin

Content overview

What is the thyroid gland and how does it work, what are thyroid function tests, how can blood tests be used to diagnose thyroid disorders, tsh and ft4, thyroid antibodies, is it necessary to repeat testing for thyroid antibodies, how can blood tests be used to manage thyroid disorders, what can affect the results of thyroid function tests, when should i have a thyroid function blood test.

Some important points

The thyroid gland lies in the front of your neck just below your Adam’s apple. It is made up of two lobes, on either side of your windpipe, joined by a small bridge of thyroid tissue called the isthmus. The thyroid secretes two main hormones into the bloodstream. One of these is thyroxine , which contains four atoms of iodine and is often called T4. This in turn is converted to tri-iodothyronine (T3), which contains three atoms of iodine. It is the T3 that is biologically active and regulates your body’s metabolism.

The amount of T4 and T3 secreted by your thyroid gland is regulated by the pituitary gland, which lies underneath your brain. The pituitary senses the level of thyroid hormones in your bloodstream, just as the thermostat in your living room senses the temperature. If the level drops just a little below normal the pituitary reacts by secreting a hormone called thyroid-stimulating hormone (TSH), which activates the thyroid gland to produce more T4. When the thyroid hormone levels rise above normal, the ‘thermostat’ senses this and the pituitary stops secreting TSH so that the thyroid makes less T4. TSH is also called thyrotropin .

The usual blood tests done for thyroid function are TSH, T4 and sometimes T3.

In most cases, your TSH level will be the first hormone to be measured, because if this is normal, it is very likely that your thyroid is functioning normally. The exception to this is when a pituitary problem is suspected, in which case T4 should be measured as well.

It is good practice for doctors to measure the T4 in addition to the TSH in children, as T4 is essential to brain development.

Many laboratories use a ‘cascade’ system, so the other hormones will be measured if the TSH is not normal.

• If the TSH level is above the reference range, the blood T4 will be measured.
• If the TSH level is below the reference range, the blood T4 and T3 will be measured.

 A blood sample is taken from a vein in the arm and sent off to the laboratory for analysis. Usually the ‘free’ or active portion of T4 and T3 is measured (i.e., FT4 and FT3). Laboratories use reference ranges to compare blood test results with results in the normal healthy population. Typical reference ranges for healthy adults are:

These ranges are only a guide and will vary according to laboratory. In pregnancy the serum TSH reference range is different from the general population and should ideally be based on reference ranges derived from healthy pregnant women in the same population. Follow this link to see our leaflet: Your Guide to Pregnancy and Fertility in Thyroid Disorders .

There are different reference ranges for testing babies and young children.

Your doctor will interpret these tests, together with your symptoms and how you feel, in order to diagnose whether you have a thyroid disorder, how severe it is, and how to treat it. If your TSH and FT4 results are outside the reference range your doctor may order additional tests. Current guidelines do not advise the use of thyroid hormone replacement if thyroid hormone levels are within normal limits.

If the TSH level is high and the FT4 result is low this suggests an underactive thyroid ( hypothyroidism ) that requires treatment.

If the TSH level is low and the FT4 result is high this suggests an overactive thyroid ( hyperthyroidism ) that requires treatment.

If the TSH level is slightly raised but the FT4 level is still within the normal reference range this is called subclinical hypothyroidism or mild thyroid failure. It may gradually develop into full-blown or clinical hypothyroidism over many years; an additional test for thyroid antibodies will help to determine the risk. Some people with subclinical hypothyroidism, particularly those whose TSH level is greater than 10mU/l or women who are trying to become pregnant, may benefit from treatment with levothyroxine.

A low TSH with a low FT4 may be a result of a failure of the pituitary gland (secondary hypothyroidism caused by hypopituitarism) or a response to any significant illness that doesn’t involve your thyroid.

This is usually only used in testing for hyperthyroidism or assessing its severity.

If the initial thyroid test results show signs of a thyroid problem and if there is a suspicion of an autoimmune thyroid disease, one or more thyroid antibody tests may be ordered. Antibody tests are used to confirm the diagnosis of autoimmune thyroid diseases. Some people will test positive for more than one type of thyroid antibody.

In people with subclinical thyroid disease the presence of antibodies can indicate that a person may go on to develop full-blown thyroid disease in the future, but that treatment is not yet required. 

Positive antibodies can also be present in people without thyroid disease.

It is rarely useful to repeat measurements of TPOAb and Tg Ab in adults and their level does not usually influence the treatment given. In children, antibodies may be tested when they move from paediatric to adult care in cases where the underlying cause of the thyroid dysfunction has not been established.

In contrast, measurements of TSHR Ab can be used to guide treatment decisions in Graves’ disease (autoimmune thyroid overactivity). For example, relapse of Graves' disease is more likely if anti-thyroid medicines are stopped when TSHR Abs are still elevated.

Other more specialised tests are thyroglobulin (Tg) (used in monitoring people who have already been treated for differentiated thyroid cancer) and calcitonin (used in monitoring people with medullary thyroid cancer, or rarely as part of the diagnosis of thyroid disease where medullary cancer is suspected).

The aims of treatment are to make you feel better and to ensure that you come to no long-term harm from your thyroid hormone replacement. The blood test for TSH, which is the most sensitive marker of your thyroid status, is used as a biochemical marker to ensure that your thyroid hormone replacement is adequate.

It is recommended that patients on thyroid hormone replacement should keep their TSH within the reference range. Over-replacement (e.g. if the TSH becomes undetectable) may cause osteoporosis and long-term harm to the cardiovascular system. The target is different in thyroid cancer where the aim in selected patients is to keep the TSH level just below the reference range (usually to 0.1-0.5mU/L) for a period of time.

It is preferable to avoid having TSH levels that are either below or above the reference range during treatment for hypothyroidism. This is because population studies show that there is a slightly lower life expectancy and a small increased risk of health problems in the long-term for people who are both overtreated and undertreated with levothyroxine. If you have thyroid blood tests that are outside the reference range over a long period of time, you should discuss these small risks with your doctor. 

Within the limits described above, it is recommended that you and your doctor set individual targets that are right for your particular circumstances.

If you have been diagnosed with hypothyroidism you will start treatment with levothyroxine - a synthetic version of the thyroxine (T4) produced by the thyroid gland.

If you have hyperthyroidism the available treatments are antithyroid drugs to reduce the production of thyroid hormones; surgery to remove all or part of the thyroid gland; or radioactive iodine to reduce the activity of the thyroid. Your doctor will discuss treatment options with you.

At the start of treatment your doctor will carry out blood tests usually every few weeks. The results will help to fine-tune your treatment. You will normally have less frequent tests when you are stable on your treatment. In hypothyroidism , a TSH test once a year will check that levels are within the reference range. In hyperthyroidism the usual tests are TSH and FT4; how often these take place will depend on the treatment.

You will have additional tests if the results are abnormal, and you should tell your doctor about any change in your health between blood tests. If your results are normal, but you still don’t feel entirely well, ask your doctor whether there is room for a slight adjustment of your dose. This can be considered if your TSH level can be kept within the reference range. You should not, however, alter your dose without discussing this with your doctor.

Once you start on levothyroxine it may take several months before your symptoms improve even if the tests results are satisfactory. This is especially the case in patients with a history of Graves’ disease who may have been hyperthyroid for many months and who may take a considerable time to adjust to feeling ‘normal’ with satisfactory test results following radioiodine or surgery.

Thyroid function tests can be influenced by medications and illnesses. Let the person taking your blood test know of anything that might affect the readings, especially:

• Any serious illness such as heart attack, infection, trauma, serious liver disease or kidney failure
• Medication used to treat thyroid disorders, especially when taking too much or too little
• Any other medication you are taking, including: the contraceptive pill, steroid hormones, anticonvulsants, anti-inflammatory drugs, lithium (used for certain mental disorders) and amiodarone (used to control irregularities of the heart beat) and any mineral or vitamin supplements particularly if the preparation contains iodine or biotin.

You should make an appointment with your GP and ask for a blood test if you have:

• Symptoms of an over- or underactive thyroid
• Swelling or thickening in the neck
• An irregular or fast heart rate
• High cholesterol (which causes atherosclerosis – a build-up of fat in the arteries)
• Osteoporosis (fragile or thinning bones)
• Fertility problems, abnormal menstrual cycles, recurrent miscarriage, low libido
• Family history of autoimmune disorders, e.g., type 1 diabetes, vitiligo, etc

Or if you are

• Feeling unwell after having a baby
• Planning pregnancy or in early pregnancy (and you have a family history or personal history of thyroid disorders, a past history of postpartum thyroiditis, or type 1 diabetes)

You should have a blood test once a year, or more frequently if your doctor advises, if:

• You have a diagnosed thyroid disorder
• You have had previous treatment for an overactive thyroid (radioactive iodine, thyroid surgery, medication)
• You have had irradiation to the head and neck after surgery for head and neck cancer
• Before you have treatment with amiodarone,  lithium or alemtuzumab then 6-12 months during treatment and 12 months after treatment

People with Down’s syndrome , Turner syndrome , Addison’s disease or other autoimmune diseases should also be tested regularly.

Some important points….

• Blood tests are currently the most accurate way to diagnose and manage thyroid disorders
• Your symptoms and how you feel are an important part of the diagnosis
• It is important for your health that the TSH level is within the reference range
• It is rarely necessary to repeat antibody tests in Hashimoto’s disease
• If you are taking medication for a thyroid disorder, there may be scope to fine-tune your treatment so that you feel better
• If you have a diagnosed thyroid disorder or have had previous treatment for an overactive thyroid, it is important to have a blood test every 12 months, or as advised by your doctor
• If you have a thyroid disorder you should have a blood test in early pregnancy or if you are planning a pregnancy
• If you are taking medication, do not alter your dose without discussing this with your doctor

Thyroid problems often run in families and if family members are unwell they should be encouraged to discuss with their own GP whether thyroid testing is warranted.

If you have questions or concerns about your thyroid disorder, you should talk to your doctor or specialist as they will be best placed to advise you. You may also contact the British Thyroid Foundation for further information and support, or if you have any comments about the information contained in this leaflet.

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What Is a T4 Test?

What is free t4 and bound t4.

T4 stands for thyroxine, one of two hormones your thyroid gland makes. The thyroid is a butterfly-shaped gland in your neck that helps control your body's growth and energy use. The T4 test measures the amount of T4 in your blood to show whether your thyroid works as well as it should. 

You have two kinds of T4 hormone:

• Free T4 travels around your bloodstream on its own and goes wherever you need it.
• Bound T4 attaches to proteins to travel through your blood.

A total T4 test measures both free and bound T4. A free T4 test measures only thyroxine that's not bound to proteins. Many doctors today use the free T4 test because it's more accurate than the test for bound T4.

The T4 test can also detect problems with your pituitary gland . This gland releases TSH (thyroid-stimulating hormone) that directs the thyroid to release its hormones. 

The information that follows will help you understand why your doctor has asked for a T4 test. It will also help you know what the results might mean in terms of your own health.

Why You Might Have a T4 Test

Your doctor may order a T4 test if: 

• You have symptoms of a thyroid problem.
• Your thyroid gland is swollen.
• You had an abnormal result on a TSH test.

Or you might have this test if your doctor has already diagnosed you with a thyroid disease and wants to see how well your treatment is working.

The T4 test helps your doctor diagnose hypothyroidism and hyperthyroidism .

Hypothyroidism is an underactive thyroid gland. That means your thyroid produces too little of its hormones, which slows your body down. Symptoms of hypothyroidism include:

• Feeling cold
• Weight gain
• Constipation
• Weak muscles
• Irregular periods 

Hyperthyroidism is an overactive thyroid gland. Your thyroid produces too much hormone and your body speeds up. Symptoms of hyperthyroidism include:

• Fast heart rate
• Increased appetite
• Weight loss without trying
• Anxiety , nervousness
• Shaky hands
• Feeling hot
• Trouble sleeping
• Dry, puffy eyes
• Thin hair that breaks easily

The T4 Blood Test Procedure

How to prepare.

You don't need to do anything special before this test. But, do tell your doctor about any medicines or supplements you take -- even ones you bought without a prescription. Some drugs , including seizure medicines, heart drugs, and birth control pills , can affect test results. The supplement biotin can cause a false-positive result, where your test results are abnormal but you don't really have a thyroid problem.

Also tell your doctor if you've been sick. Some infections can alter your test results. You may need to wait until you feel better to have this test. Chronic diseases like kidney failure and cirrhosis may also affect T4 test results.

What to Expect

The T4 test is a blood test. Your health care provider will use a needle to draw blood from a vein in your arm. You may feel a slight prick as the needle goes in. Afterward, the provider will remove the needle and place a bandage over the site.

What Your T4 Blood Test Results Mean

You should get the results of your test within a day or so. Results can vary based on your age, gender, and the method your lab uses to read the result.

Normal Range

The normal range for free T4 in adults is 4.6 to 11.2 micrograms per deciliter (mcg/dL). 

A normal T4 test result means your thyroid gland works like it should.

High or Low T4

A high T4 result could mean you have hyperthyroidism. A low T4 test result is a sign of hypothyroidism. 

Your hypothalamus and pituitary glands control the release of T4. An abnormal result on the T4 test could also be a sign of a problem with one of these glands.

Other Thyroid Tests You Might Need

To help your doctor diagnose the exact problem you have, you may also need tests of the following:

• T3 -- the other hormone your thyroid gland makes, works with T4 to control your body's energy use
• Thyroid-stimulating hormone (TSH) -- a hormone your pituitary gland makes, tells your thyroid to make T3 and T4
• Thyroid antibodies -- proteins your immune system makes if it mistakenly sees your thyroid gland as foreign, like in Hashimoto's thyroiditis or Graves' disease

T4 Blood Test Side Effects

The T4 test is just a basic blood test. Any side effects it might cause are minor, including:

• Pain from the needle stick
• Dizziness or fainting
• A lump under the skin

After Your T4 Lab Test

Your test results will help your doctor decide what you should do next. If your results are normal, you may not need to do anything else. An abnormal result on this and other thyroid tests may mean you need treatment for a thyroid condition.

Thyroxine (T4) Test

A thyroxine test helps diagnose disorders of the thyroid. The thyroid is a small, butterfly-shaped gland located near the throat. Your thyroid makes hormones that regulate the way your body uses energy. It also plays an important role in regulating your weight, body temperature, muscle strength, and even your mood. Thyroxine, also known as T4, is a type of thyroid hormone. This test measures the level of T4 in your blood. Too much or too little T4 can indicate thyroid disease .

The T4 hormone comes in two forms:

• Free T4 , which enters the body tissues where it's needed
• Bound T4 , which attaches to proteins, preventing it from entering body tissues

A test that measures both free and bound T4 is called a total T4 test. Other tests measure just free T4. A free T4 test is considered more accurate than a total T4 test for checking thyroid function.

Other names: free thyroxine, free T4, total T4 concentration, thyroxine screen, free T4 concentration

A T4 test is used to evaluate thyroid function and diagnose thyroid disease.

Thyroid disease is much more common in women and most often occurs under the age of 40. It also tend to run in families. You may need a thyroxine test if a family member has ever had thyroid disease or if you have symptoms of having too much thyroid hormone in your blood, a condition called hyperthyroidism , or symptoms of having too little thyroid hormone, a condition called hypothyroidism .

Symptoms of hyperthyroidism, also known as overactive thyroid, include:

• Weight loss
• Tremors in the hands
• Increased heart rate
• Bulging of the eyes
• Trouble sleeping

Symptoms of hypothyroidism, also known as underactive thyroid, include:

• Weight gain
• Low tolerance for cold temperatures
• Irregular menstrual periods
• Constipation

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

You don't need any special preparations for a thyroxine blood test. If your health care provider has ordered more tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test. Your health care provider will let you know if there are any special instructions to follow.

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

Your results may come in the form of total T4, free T4, or a free T4 index.

• The free T4 index includes a formula that compares free and bound T4.
• High levels of any of these tests (total T4, free T4, or free T4 index) may indicate an overactive thyroid, also known as hyperthyroidism.
• Low levels of any of these tests (total T4, free T4, or free T4 index) may indicate an underactive thyroid, also known as hypothyroidism.

If your T4 test results are not normal, your health care provider will likely order more thyroid tests to help make a diagnosis. These may include:

• T3 thyroid hormone tests. T3 is another hormone made by the thyroid.
• A TSH (thyroid stimulating hormone) test. TSH is a hormone made by the pituitary gland. It stimulates the thyroid to produce T4 and T3 hormones.
• Tests to diagnose Graves' disease, an autoimmune disease that causes hyperthyroidism
• Tests to diagnose Hashimoto's thyroiditis, an autoimmune disease that causes hypothyroidism

Learn more about laboratory tests, reference ranges, and understanding results .

Thyroid changes can happen during pregnancy . Although it is not common, some women can develop thyroid disease during pregnancy. Hyperthyroidism happens in about 0.1% to 0.4% of pregnancies, while hypothyroidism happens in approximately 2.5% of pregnancies. 

Hyperthyroidism, and less often, hypothyroidism, may remain after pregnancy. If you develop a thyroid condition during pregnancy, your health care provider will monitor your condition after your baby is born. Also, if you have a history of thyroid disease, be sure to talk with your health care provider if you are pregnant or are thinking of becoming pregnant.

• American Thyroid Association [Internet]. Falls Church (VA): American Thyroid Association; c2017. Thyroid Function Tests [cited 2017 May 22]; [about 2 screens]. Available from: https://www.thyroid.org/thyroid-function-tests
• Hinkle J, Cheever K. Brunner &amp; Suddarth's Handbook of Laboratory and Diagnostic Tests. 2 nd Ed, Kindle. Philadelphia: Wolters Kluwer Health, Lippincott Williams &amp; Wilkins; c2014. Thryoxine, Serum 485 p.
• Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2017. Free T4: The Test [updated 2014 Oct 16; cited 2017 May 22]; [about 4 screens]. Available from: https://labtestsonline.org/understanding/analytes/t4/tab/test
• Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2017. Free T4: The Test Sample [updated 2014 Oct 16; cited 2017 May 22]; [about 3 screens]. Available from: https://labtestsonline.org/understanding/analytes/t4/tab/sample
• Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2017. TSH: The Test Sample [updated 2014 Oct 15; cited 2017 May 22]; [about 3 screens]. Available from: https://labtestsonline.org/understanding/analytes/tsh/tab/sample
• Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck &amp; Co. Inc.; c2017. Overview of the Thyroid Gland [cited 2017 May 22]; [about 2 screens]. Available from: https://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/thyroid-gland-disorders/overview-of-the-thyroid-gland
• National Institute of Diabetes and Digestive and Kidney Diseases [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Graves' Disease; 2012 Aug [cited 2017 May 22]; [about 3 screens]. Available from: https://www.niddk.nih.gov/health-information/endocrine-diseases/graves-disease
• National Institute of Diabetes and Digestive and Kidney Diseases [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Hashimoto's Disease; 2014 May [cited 2017 May 22]; [about 3 screens]. Available from: https://www.niddk.nih.gov/health-information/endocrine-diseases/hashimotos-disease
• National Institute of Diabetes and Digestive and Kidney Diseases [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Thyroid Tests; 2014 May [cited 2017 May 22]; [about 3 screens]. Available from: https://www.niddk.nih.gov/health-information/diagnostic-tests/thyroid
• National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; What Are the Risks of Blood Tests? [updated 2012 Jan 6; cited 2017 May 22]; [about 5 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests#Risk-Factors
• National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; What To Expect with Blood Tests [updated 2012 Jan 6; cited 2017 May 22]; [about 4 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests
• Soldin OP. Thyroid Function Testing in Pregnancy and Thyroid Disease: Trimester-specific Reference Intervals. Ther Drug Monit. [Internet]. 2006 Feb [cited 2019 Jun 3]; 28(1):8-11. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3625634
• University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2017. Health Encyclopedia: Free and Bound T4 [cited 2017 May 22]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&amp;contentid;=t4_free_and_bound_blood
• University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2017. Health Encyclopedia: Free T4 [cited 2017 May 22]; [about 2 screens]. Available from:  https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&amp;contentid=free_t4_thyroxine

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What are T3 and T4: The Complete Guide to Your Thyroid Hormones

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T3 and T4 are hormones that are secreted by your thyroid gland and have a major impact on your health. T4 is the thyroid hormone thyroxine and T3 is the hormone triiodothyronine, and they affect almost every organ in your body. T4 and T3 levels in your body are regulated by the thyroid-stimulating hormone, or TSH for short. Thyroid tests to check thyroid function usually check for abnormal levels of TSH and T4 hormones.

Symptoms of hypothyroidism (underactive thyroid) are usually associated with low levels of T4 and T3. This can cause you to feel fatigued, have difficulty losing weight, feel tired, and have hair loss. An underactive thyroid is also associated with high TSH levels and low T4 levels.

An overactive thyroid or hyperthyroidism is caused by high T4 and T3 levels in your bloodstream. When your thyroid secretes too much thyroid hormones you can feel restless, suffer from sleep problems, have frequent digestive upset, and increased sweating. If you suffer from hyperthyroidism, your thyroid test results will usually show low levels of TSH hormone .

This article contains a complete guide to your thyroid hormones and thyroid function. You will learn what T4 and T3 hormones do in your body and what the target range of T3 and T4 is. I will also explore why testing for free T4 levels is sometimes better than a TSH blood test.

The Thyroid Gland and What it Does

Your thyroid is an important hormonal gland in the body that has a direct impact on your metabolism. Your thyroid sits in the front part of your neck just below your voice box and is shaped like a butterfly.

Dr. Carol DerSarkissian on WebMD says that the thyroid releases hormones into the bloodstream. Your thyroid releases triiodothyronine (T3), thyroxine (T4), and calcitonin (produced by the parathyroid glands). From these, Dr. DerSarkissian says that T4 is the main hormone that affects growth, metabolism, and brain development. 1

What is TSH?

Your thyroid function depends on hormones that are released by glands at the base of your brain. The hypothalamus releases thyrotropin-releasing hormone (TRH) which then stimulates the pituitary gland. The pituitary gland then secretes TSH that stimulates the thyroid to produce T3 and T4 hormones which are released into your bloodstream.

Doctors from the Cleveland Clinic explain that TSH levels can fluctuate depending on T3 and T4 levels in blood serum. For example, if your thyroid doesn’t produce enough thyroid hormones (underactive thyroid), messages are sent to your pituitary gland to increase TSH levels. On the other hand, high levels of T4 and T3 hormones caused by an overactive thyroid can signal your brain to lower TSH. 2

The journal Frontiers in Endocrinology describe this connection between T3, T4, and TSH as a feedback loop. Doctors say that TSH testing may not be the most accurate way to monitor thyroid health if you receive T4 thyroid replacement therapy for hypothyroidism . 3

What are T3 and T4?

T3 is the thyroid hormone triiodothyronine and T4 is the thyroid hormone thyroxine.

The British Thyroid Foundation says that T3 and T4 are the two main hormones that your thyroid gland secretes. Together they affect and influence almost every cell in your body. Your thyroid usually produces more T4 hormone than T3, but T4 is converted to T3 when it reaches cells and tissues in your body. Therefore, T4 is the more important hormone to measure when testing for thyroid dysfunction. 4

Let’s look in more detail at what T3 does and why T4 is the more potent hormone.

What is T3?

Doctors from the Mayo Clinic say that triiodothyronine (T3) has 3 iodine molecules in its structure. This is secreted directly by the thyroid gland and is classed as the most powerful thyroid hormone. This is because it is more metabolically active when controlling your body’s metabolism, temperature, and digestive system. 5

What is Free T3 (FT3)?

Thyroid hormone binds to proteins in your body and any that isn’t is classed a free T3. The British Thyroid Foundation says that free T3 is the active part of triiodothyronine. The level of FT3 can help to diagnose hyperthyroidism and monitor replacement T3 therapy. 6

What is T3 Uptake?

Sometimes, you may hear doctors talking about T3 uptake when discussing thyroid testing. What is T3 (T3RU) uptake? The book Clinical Methods says that T3RU (T3 uptake) test measures the levels of proteins in the blood that carry thyroid hormone. 7 T3 uptake can help your doctor interpret the results of T3 and T4 blood tests. The T3RU test is hardly used these days because the TBG ( thyroxine-binding globulin ) and the free T4 blood tests are now available.

What is T4?

The thyroid gland also secretes T4, but in larger quantities than T3. Thyroxine (T4) has 4 iodine molecules attached to its molecular structure. When T4 gets into the cells of the body, it loses one molecule and becomes T3. Thyroid function tests that check both TSH and T4 levels are the most accurate ways to diagnose thyroid conditions. 8

What is Free T4 (FT4)?

Similar to free T3, free thyroxine (T4) levels are the unbound levels of T4 hormone (the active part of thyroxine). You have more free T4 (FT4) in your blood than FT3. High T4 levels or low T4 levels can help to accurately diagnose hyperthyroidism or hypothyroidism. The book Clinical Methods says that blood tests for both TSH and T4 help to accurately assess thyroid health. 7

The amount of free T4 helps doctors see how much thyroid gland hormone is available in your blood to meet your energy requirements.

Normal Levels of T3 and T4

If you show signs of abnormal thyroid function , doctors may arrange for a blood test to check FT4 levels and possibly free T3. This is usually done at the same time as a TSH blood test, or doctors may check T4 levels only if TSH blood test readings are abnormal.

Normal T3 levels (Normal Free T3 Levels and Total T3)

Dr. Jayita Poduval, who is an Ear, Nose, and Throat (EAT) specialist, says that the normal total T3 and free T3 ranges are as follows: 9

Total T3 (triiodothyronine) range:

• Children : 125 – 250 ng/dL
• Adults : 80 – 220 ng/dL

Normal free T3 (FT3) range:

• Adults : 260 – 460 pg/dL (4 – 7.4 pmol/L)

Normal T4 levels (Normal Free T4 Levels and Total T4)

Testing for normal levels of T4 thyroid hormone is a common lab test along with TSH to diagnose thyroid issues. Dr. Muhammad Bader Hammami on Medscape says that total T4 (TT4) range and free T4 (FT4) range are as follows: 10

Total T4 (TT4) range:

• Newborn babies up to 14 days old : 11.8 – 22.6 mcg/dL (152 – 292 nmol/L)
• Babies and older children : 6.4 – 13.3 mcg/dL (83 – 172 nmol/L)
• Adults : 5.4 – 11.5 mcg/dL (57 – 148 nmol/L)

Normal free T4 (FT4) range:

• Children and adolescents : 0.8 – 2 ng/dL (10 – 26 pmol/L)
• Adults : 0.7 – 1.8 ng/dL (9 – 23 pmol/L)
• Pregnant women : 0.5 – 1.0 ng/dL (6.5 – 13 pmol/L)

How TSH Affects T3 and T4 Levels

TSH, T4, and T3 are all connected with your thyroid function and TSH can affect thyroid hormone levels in your blood. TSH levels that are less than the normal range often indicate hyperthyroidism because your thyroid is overproducing T3 and T4. If your lab test results show high TSH levels , this can indicate that your thyroid is sluggish and there is not enough thyroid hormones.

To learn what your TSH levels mean, read my complete guide to TSH levels (including optimal thyroid levels) .

High T3 and T4

Having lab test readings that show high T3 and T4 can mean that you have hyperthyroidism. Doctors will usually test FT4 levels and may also run FT3 tests if your TSH readings are low.

High T3 Symptoms

Dr. Stephanie Lee on eMedicineHealth says that significantly higher than normal T3 can be a sign of severe hyperthyroidism. 11 According to the journal Clinical Endocrinology , Graves’ disease is a common cause of severe hyperthyroidism. This can cause symptoms like: 12 , 13

• Bulging eyes
• Thick red skin on the tops of your feet
• Inflamed eyes with a gritty feeling
• Increased sensitivity to light

High T4 symptoms

If your T4 test readings are too high, it can mean you have hyperthyroidism. According to Dr. Oliver Starr on Patient.info, classic signs of an overactive thyroid gland that secretes too much T4 hormone can include any of the following: 14

• Increased irritability and restlessness
• Poor sleeping habits and difficulty getting to sleep
• Runny stools because your digestive system is working too quickly
• Losing weight without trying
• Thinning hair
• Increased sweating
• Light menstrual periods
• Shortness of breath

Low T3 and T4

When levels of T3 and T4 fall below the normal range, you will probably show signs of hypothyroidism. Mild hypothyroidism can even occur if your TSH readings are within the normal range.

Low T4 Symptoms

Dr. Gabriel Bucurescu on Medscape says that classic symptoms of an underactive thyroid that doesn’t produce enough thyroid hormone can include: 15

• Feelings of weakness and fatigue
• Dry skin and hair
• Weight gain
• Problems with memory and concentration
• Tingling in the fingers or a feeling of ‘pins and needles’ in the feet
• Intolerance to the cold

Low T3 Symptoms

Usually, low T3 levels in a thyroid function test are matched by low T4 readings and elevated TSH levels. Therefore, T3 below the normal range usually means a person has hypothyroidism.

According to doctors from the American Association for Clinical Chemistry, it would be rare when blood tests show low T3 with low TSH and high T4. 16

How TSH is Connected with T3 and T4 Levels

Dr. Oliver Starr on Patient.info explains that all your thyroid hormones and TSH (thyroid-stimulating hormone) need to work in balance. This forms what doctors call a feedback loop where the levels of thyroid hormone in your blood signal to your brain to produce more or less TSH. 17

For example, if an overactive thyroid produces too much T4 or T3, the feedback loop to your brain signals to produce less TSH. The same is true if your thyroid isn’t working properly and produces too little hormone.

Doctors from the National Health Service explain the basic relationship between TSH and thyroid hormone levels: 18

• Hypothyroidism : TSH high, T4 low, and T3 low or normal
• Hyperthyroidism : TSH low, T4 high or normal, and T3 high or normal
• Subclinical thyroid disease : Levels of T4 and T3 are normal but TSH is either too high or too low
• Non-thyroidal illness : TSH low, T4 low or normal, and T3 low or normal

High (Elevated) TSH and Normal T4

Lab test results that show TSH levels greater than 4.0 mU/L and T4 within the normal range can indicate subclinical hypothyroidism.

According to the journal American Family Physician , subclinical hypothyroidism could show that person is at greater risk of developing an underactive thyroid disorder. This often happens in older women and there may be no visible symptoms. Doctors treat subclinical hypothyroidism on an individual basis as thyroid hormone replacement can lead to osteoporosis. 19

High TSH and Low T4

Blood test results that show TSH levels higher than the normal range and FT4 of less than 0.7 ng/dL mean that you have an underactive thyroid.

Dr. Laura J. Martin on WebMD says that some of the causes of hypothyroidism can include: 20

• Hashimoto’s thyroiditis (Hashimoto’s disease) which is an autoimmune disorder that attacks the thyroid gland
• Inflammation of the thyroid gland
• Radiation treatment for cancer
• A lack of iodine in the diet
• Pregnancy can also cause high TSH and low T4 readings

Low TSH and High T4

Test result reading of TSH of less than 0.4 mIU/L and FT4 more than 1.8 ng/dL means that your thyroid is overactive. Hyperthyroidism is less common that an underactive thyroid, however, similar to hypothyroidism, it affects women more than men.

Dr. Carol DerSarkissian on WebMD says that some conditions that are linked to hyperthyroidism can include: 21

• Antibodies in your blood that affect your thyroid (as in Graves’ disease)
• Noncancerous growths in your thyroid that cause it to swell and produce more T4
• An autoimmune condition
• Receiving too much thyroid replacement hormone

Normal TSH and Low T4

In some cases, TSH test results are within the normal range but low T4 results can occur. Dr. Louise Newson on Patient.info says that this can often happen in people who are chronically ill. The illness may affect a person’s metabolism which affects their thyroid hormone levels. This means that the pituitary gland is secreting TSH within the normal range and the thyroid is working properly. However, thyroid hormones in the body are lacking. 22

Also, if you have recently had treatment for hyperthyroidism, you could have normal TSH but low T4.

Treating Hypothyroidism with Replacement T4 and T3

Doctors treat the symptoms of hypothyroidism by prescribing oral thyroid hormone replacement therapy. Some treatments for an underactive thyroid involve prescribing T4 replacements like levothyroxine sodium (brand names: Levothroid, Levoxyl, Synthroid, or Tirosint). Other treatments involve a combination of T4 and T3 replacement therapy.

According to a study in the Journal of Clinical Endocrinology and Metabolism , there is a move towards using combined replacement of T4 and T3 therapies. Some doctors prefer this because the combined T4 and T3 thyroid treatments may have less impact on quality of life and treat hypothyroidism better. 23

Tests for Measuring T4 and T3

The British Thyroid Foundation says that testing for thyroid dysfunction can include one or more of the following tests: 6

• Testing to see if free thyroxine (FT4) is within the range of 0.7 – 1.8 ng/dL
• Free triiodothyronine (FT3) tests for the range of 260 – 480 pg/dL
• TSH and FT4 test
• Testing for thyroid antibodies to diagnose Graves’ disease or Hashimoto’s disease

Doctors recommend testing for T4 and T3 as part of a thyroid function test if you have any of the following symptoms:

• Fast or irregular heartbeat
• Thickening around the base of the neck
• High cholesterol
• Osteoporosis
• Feel unwell after having a baby

Read these related articles:

• How to Test Your Thyroid With a Thermometer
• TSH Levels: Normal, High, or Low (Including Optimal Thyroid Levels)
• 1 Minute At Home Thyroid Cancer Self-Test: This Can Save Your Life

Medical Sources:

• WebMD . Picture of the thyroid.
• ClevelandClinic . Thyroid blood tests.
• Front Endocrinol (Lausanne) . 2015; 6: 177.
• BTF-Thyroid . Your thyroid gland.
• MayoMedicalLaboratories . Test ID: T3
• BTF-Thyroid . Thyroid function tests.
• NCBI . Thyroid function tests.
• MedicineNet . Medical definition of thyroxine.
• Medscape . Triiodothyronine.
• Medscape . Thyroxine.
• eMedicineHealth . Hyperthyroidism.
• Clin Endocrinol (Oxf). 2010 Apr;72(4):551-7.
• MayoClinic . Graves’ disease.
• PatientInfo . Overactive thyroid gland.
• Medscape . Neurological manifestations of thyroid disease.
• LabTestsOnline . Free T3 and total T3.
• PatientInfo . Thyroid function tests.
• CamdenCCG . Abnormal thyroid function tests.
• Am Fam Physician . 2001 Nov 15;64(10):1717-1725.
• WebMD . Hypothyroidism.
• WebMD . Hyperthyroidism.
• J Clin Endocrinol Metab. 2012 Jul;97(7):2256-71.

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Healthy and Natural World

Thyroid Blood Tests: Free T4 & TSH Levels

Pedro Pinheiro, MD

Updated January 22, 2024

comment 2 Comments

Summary of the Article : TL;DR

• What is the thyroid? : A butterfly-shaped gland located in the neck, it produces thyroid hormones (T3 and T4).
• What is hypothyroidism? : A condition in which there is insufficient production of thyroid hormones.
• What is hyperthyroidism? : A condition in which there is an excess production of thyroid hormones.
• Diagnosis : Made through the measurement of thyroid hormones in the blood, mainly TSH and free T4.
• What are Free T4 and Free T3? : Active fractions of the T3 and T4 hormones, which effectively modulate metabolism.
• What is TSH? : A pituitary hormone, it regulates the production of T3 and T4 by the thyroid.
• Normal TSH values : 0.4 to 4.5 mU/L.
• Normal Free T4 values : 0.7 to 1.8 ng/dl.
• What elevated TSH indicates : Usually hypothyroidism, but can also be a pituitary issue.
• What very low TSH indicates : Usually hyperthyroidism, but can also be a pituitary issue.

Hypothyroidism and Hyperthyroidism

Hypothyroidism is a condition caused by an underactive thyroid gland, resulting in insufficient production of thyroid hormones. Hyperthyroidism, on the other hand, is a condition caused by an overactive thyroid gland, resulting in an excess production of thyroid hormones.

Although hypothyroidism and hyperthyroidism are different diseases and have different symptoms, both are diagnosed by measuring thyroid hormone levels in the blood, specifically TSH and free T4.

In this article, we’ll explain the thyroid hormones and how to interpret their levels in blood tests.

How Does the Thyroid Gland Work?

The thyroid is a butterfly-shaped gland located at the base of the neck. It captures iodine consumed in food and combines it with an amino acid called tyrosine to synthesize two hormones known as triiodothyronine (T3) and thyroxine (T4).

The T3 and T4 synthesized by the thyroid are released into the bloodstream, where they act on all the cells of our body, regulating their metabolism, dictating how cells transform oxygen, glucose, and calories into energy.

• When the thyroid produces too much T3 and T4, our metabolism speeds up.
• When the thyroid produces too little T3 and T4, our metabolism slows down.

Generally, of the total hormones produced by the thyroid, 80% are T4 and 20% are T3. Although produced in smaller quantities, T3 is a much more potent hormone than T4, with its blood concentration directly dictating the body’s metabolic rate.

T4 is actually a prohormone, meaning it is a precursor to T3. 80% of the T4 released into the bloodstream, when reaching organs or tissues such as the liver, kidneys, spleen, muscles, or fat, is converted into T3 to be utilized by the cells.

Therefore, T3 is the thyroid hormone that effectively acts in our body, originating predominantly from circulating T4. Only a tiny portion of the active T3 is directly produced by the thyroid.

What is Free T4?

Over 99% of circulating T4 and T3 are bound to a protein called thyroxine-binding globulin (TBG).

These TBG-bound hormones are inert and cannot be used by organs and tissues. Therefore, only a tiny fraction, called free T4 and free T3, are chemically active and can modulate the body’s metabolism. Only free T4 can be transformed into T3 in organs and tissues.

In summary:

• The T3 hormone is the one that effectively acts on body cells, modulating metabolism.
• Most of the active T3 is derived from the conversion of T4 in peripheral tissues.
• Since more than 99% of T4 is bound to TBG, only a tiny fraction of free T4, less than 1%, provides T3 for the body’s organs and tissues to use in their cells.

In conclusion, measuring free T4 in the blood is the test that really gives us an idea of how much potentially viable thyroid hormone is in the circulation. If there is too much circulating free T4, there will be too much T3 production in the organs, leading to hyperthyroidism. If there is too little circulating free T4, there will be a lack of T3 in the tissues, resulting in hypothyroidism.

In clinical practice, the measurement of free T4 is more valuable than the measurement of T3 or free T3 in most cases.

What is the Role of TSH?

The amount of T3 and T4 produced by the thyroid gland is carefully regulated by the central nervous system, specifically the pituitary gland, located at the base of the brain.

In people with a healthy thyroid gland, the amount of free thyroid hormone in the blood is kept at a level that is neither too high nor too low. When there is too much free T4 in the blood, the thyroid gland reduces its production of T3 and T4. On the other hand, if there are signs that free T4 levels are becoming insufficient, the thyroid gland quickly begins producing more T3 and T4 to keep the body’s metabolism from slowing down.

The signal for the thyroid to increase or decrease its production of T3 and T4 comes from the pituitary gland, via a hormone called thyroid stimulating hormone (TSH).

See the figure above and follow the reasoning. When circulating levels of thyroid hormones (T3 and T4) are low, the pituitary gland detects this shortage and responds by increasing the secretion of Thyroid Stimulating Hormone (TSH). This elevation in TSH signals the thyroid gland to enhance the production of T3 and T4.

As the concentrations of T3 and T4 rise to optimal levels, the pituitary gland recognizes this equilibrium and correspondingly decreases TSH production. This reduction in TSH lessens the stimulation of the thyroid gland, thereby preventing the overproduction of thyroid hormones.

The interplay between TSH and free T4 levels is a finely tuned mechanism. The pituitary gland continually adjusts TSH concentrations to maintain a delicate balance. It ensures sufficient thyroid hormone production to meet the body’s needs while avoiding excessive stimulation of the thyroid gland.

What are the Normal Values of TSH and Free T4?

In most cases, the TSH and free T4 measurements are enough to assess the functioning of the thyroid.

Before we explain how to interpret the results of these two hormones, we need to know their reference values (these values can vary slightly from one laboratory to another).

• Normal TSH values : 0.4 to 4.5 mU/L (some centers accept up to 5.0 mU/L as an upper value).
• Normal free T4 values : 0.7 to 1.8 ng/dl.

Note : A study by the National Academy of Clinical Biochemistry suggested that the normal range for a healthy thyroid should be up to 2.5 mU/L. This is because they found that 95% of the healthy people they tested had thyroid levels (TSH levels) between 0.4 and 2.5 mU/L. However, another study from Germany, which also carefully selected participants, found the normal range to be slightly wider, from 0.3 to 3.63 mU/L. If we start using 2.5 mU/L as the upper normal limit for TSH, it means that many more people could be diagnosed with a mild form of low thyroid function, known as subclinical hypothyroidism. However, no clear evidence exists that TSH levels between 2.5 and 5.0 mU/L are harmful. So it’s debatable whether we should label people with these levels as having a thyroid problem.

The latest method for measuring TSH is known as the Third-generation TSH chemiluminometric assays. This advanced technique is more sensitive than earlier versions, allowing it to detect very low TSH levels, down to 0.01 mU/L. This improvement means it can identify even the smallest changes in TSH levels in the body.

What Does It Mean to Have an Elevated TSH Level?

TSH levels rise whenever the pituitary gland senses a drop in circulating thyroid hormone levels.

In patients with hypothyroidism, the pituitary needs to maintain higher than normal TSH levels (above 4.5 or 5 mU/L) to constantly stimulate the thyroid to increase its production of T3 and T4.

Different Scenarios of High TSH:

Subclinical Hypothyroidism

If the thyroid disease is still mild and the elevation of TSH can stimulate the production of thyroid hormones to keep them at adequate levels, the patient will not show any symptoms, as the symptoms of hypothyroidism only appear when free T4 levels are low. This is the case of subclinical hypothyroidism, which is an early form of hypothyroidism (suggested reading: Subclinical Hypothyroidism ).

Overt hypothyroidism

If the thyroid disease is severe, no matter how much the pituitary increases TSH production, the patient’s thyroid will be unable to respond by producing more thyroid hormones to normalize blood levels. In these cases, the patient has elevated TSH, generally above 10.0 mU/L, and low levels of free T4. As their free T4 is low, the patient usually has the typical symptoms of hypothyroidism.

Patients with untreated hypothyroidism can have very high levels of TSH, sometimes above 100.0 mU/L.

Central Hyperthyroidism

This condition occurs when TSH and free T4 levels are both elevated.

The issue in this scenario is with the pituitary, not the thyroid. The pituitary produces too much TSH despite already high levels of thyroid hormones in the blood, leading to symptoms of hyperthyroidism. This pituitary-driven hyperthyroidism is less common than thyroid-related hyperthyroidism.

In Summary, What Could a High TSH Level Indicate?

• Subclinical Hypothyroidism : Mild thyroid disorder with slightly elevated TSH (5.0-10.0 mU/L) but normal thyroid hormones (T3 and T4), presenting no symptoms.
• Clinical Hypothyroidism : Advanced thyroid disease with very high TSH (often above 10 mU/L) and low T4 levels, leading to typical hypothyroidism symptoms.
• Central Hyperthyroidism : Uncommon condition where both TSH and T4 are high, caused by pituitary dysfunction, resulting in hyperthyroidism symptoms.

What Does It Mean to Have a Low TSH Level?

The logic applied to low TSH is the same as that for high TSH. If there is an abundance of thyroid hormone circulating in the blood, the pituitary gland responds by decreasing its release of TSH, thereby reducing the stimulation of the thyroid.

Similarly, there are three distinct situations that can occur when TSH levels are low:

Subclinical Hyperthyroidism

In cases where the thyroid is overactive, TSH levels plummet to halt further stimulation of the gland. In subclinical hyperthyroidism, TSH is typically below 0.4 mU/L, but free T4 levels remain normal. This occurs because the gland is highly responsive, and minimal amounts of TSH are enough for the thyroid to produce hormones. Therefore, patients usually do not show symptoms at this stage.

Overt Hyperthyroidism

Certain conditions can cause the thyroid to become excessively active and operate independently of the pituitary gland, producing hormones even without TSH stimulation.

When there’s a high level of free T4 in the bloodstream, the pituitary is essentially “inhibited”, producing almost no TSH, with blood levels below 0.1 mU/L. The patient therefore has very low levels of TSH, but high levels of free T4, resulting in overt hyperthyroidism.

Central Hypothyroidism

When both TSH and free T4 levels are low, it suggests a normally functioning thyroid that is adequately responding to reduced TSH levels.

The problem primarily resides in the pituitary gland. Despite low free T4 levels, the pituitary fails to sufficiently elevate TSH secretion to stimulate the thyroid into producing additional hormones, thus safeguarding the patient from developing hypothyroidism.

This type of hypothyroidism, stemming from the pituitary gland, is less common compared to hypothyroidism that originates directly from the thyroid.

In Summary, What Could a low TSH Level Indicate?

• Subclinical Hyperthyroidism : overactive thyroid, leading to TSH levels falling below 0.4 mU/L to minimize gland stimulation, while free T4 levels remain normal. Patients usually don’t exhibit symptoms.
• Overt Hyperthyroidism : the thyroid gland becomes excessively active and functions independently of the pituitary gland. This results in a high concentration of free T4 and extremely low TSH levels (below 0.1 mU/L), leading to obvious symptoms of hyperthyroidism due to the elevated free T4.
• Central Hypothyroidism : both TSH and free T4 levels are low, indicating a normally functioning thyroid that’s responding appropriately to reduced TSH. The underlying issue is with the pituitary gland, which fails to increase TSH production in response to low T4.
• Laboratory assessment of thyroid function  – UpToDate.
• Thyroid Function Tests  – American Thyroid Association.
• Assessment of Thyroid Function: Towards an Integrated Laboratory – Clinical Approach  – The Clinical biochemist. Reviews.
• American Thyroid Association guidelines for use of laboratory tests in thyroid disorders  – JAMA.

Dr. Pedro Pinheiro

Pedro Pinheiro holds a medical degree from the Federal University of Rio de Janeiro (UFRJ) and is a specialist in Internal Medicine and Nephrology, certified by the State University of Rio de Janeiro (UERJ) and the Brazilian Society of Nephrology (SBN). He is currently based in Lisbon, Portugal, with his credentials recognized by the University of Porto and the Portuguese Nephrology Specialty College.

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2 responses to “thyroid blood tests: free t4 & tsh levels”.

Levothyroxine (T4): This is the synthetic form of thyroxine (T4) and is the treatment of choice for hypothyroidism. It helps replace or supplement the T4 produced by the thyroid gland, which the body can convert to T3 as needed.

Liothyronine (T3): This is the synthetic form of triiodothyronine (T3). In some cases, especially when the conversion of T4 to T3 is insufficient, liothyronine may be administered to provide T3 directly.

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What Is a Thyroxine (T4) Blood Test?

What Is T4?

Thyroxine (T4) is one of the hormones made by your thyroid gland. Your thyroid gland is the small, butterfly-shaped organ in your throat that wraps around your windpipe (trachea). It makes and releases a few different hormones, including T4, that help control the following processes:

• How your body turns the food you eat into energy (metabolism)
• How fast food moves through your digestive system
• Your heart rate and body temperature
• Brain development in children
• How your muscles contract
• The rate at which your body replaces dying cells

T4 is the inactive form of your thyroid hormone; it must be changed into the active form, triiodothyronine (T3), for your organs and cells to use. The cells in a few of your organs can convert T4 into T3, including your:

• Brain and spinal cord
• Pituitary gland
• Brown fat tissue (the kind of fat that stores and burns energy to keep your body temperature stable)

Reason for a T4 Blood Test

Your doctor may have you take a T4 blood test for a few different reasons, such as:

• To help diagnose and monitor you for thyroid disease , like an underactive or overactive thyroid.
• To help diagnose for disorders in your pituitary gland, which is a walnut-sized organ in your brain that, among other hormones, makes thyroid-stimulating hormone (TSH), which tells your thyroid how much T4 and T3 to make.
• To check how well your thyroid is working if you have had an abnormal finding on other thyroid functions tests (such as a TSH or T3 test), a lump or nodule on your thyroid, an enlarged or irregular thyroid gland, or trouble getting pregnant.

Low T4 symptoms

When your thyroid is underactive, it doesn't make enough thyroid hormone for your body to function well, and your metabolism will slow down. This is called hypothyroidism .

Symptoms of hypothyroidism include:

• Inability to concentrate and remember things
• Swelling around your eyes
• Swelling in your thyroid (also called goiter)
• Severe tiredness
• Low tolerance for cold
• Weight gain
• Not feeling hungry
• Cold, dry skin
• Slow heart rate
• Shortness of breath
• Constipation
• Irregular periods

High T4 symptoms

When your thyroid is overactive, it makes too much thyroid hormone, and your metabolism speeds up. Doctors may call this hyperthyroidism.

Symptoms of hyperthyroidism may include:

• Anxiety and depression
• Restlessness
• Irritability
• Inability to sleep
• Swelling around your eyes that makes them bulge out (Graves' eye disease)
• Weight loss
• Feeling extra hungry
• Low tolerance for heat
• Raised sweating
• Fine tremors in your fingers, head, face, or tongue
• Fast heart rate
• Feeling like your heart is fluttering, pounding, or skipping beats
• High blood pressure

About the T4 Blood Test

Your body makes two different forms of T4 hormone:

• Free T4, which flows through your bloodstream without being attached to anything. This form is ready to be taken up into any cells that need thyroid hormone right away.
• Bound T4, which travels through your bloodstream by attaching to transport proteins. These transport proteins make sure your T4 gets to the places in your body it needs to go and also keeps it from getting taken up into other organs and cells along the way. Almost all the T4 your body makes is bound.

Procedures for the T4 blood test

Tell your doctor about medications, vitamins, or supplements you're taking. Medications for seizures, heart conditions , and birth control may affect the results of the test. If you take a biotin supplement, the test may show that you have a higher T4 level than you actually do. This may cause your doctor to miss that you have a thyroid problem.

Tell your doctor if you are pregnant or have any medical conditions or infections because they may affect your test results. This includes chronic diseases like kidney failure or cirrhosis. Cirrhosis is scarring on your liver which can be caused by different diseases and conditions, including hepatitis and alcoholism. If you have a short-term infection, your doctor may want to wait to do the test until you feel better.

T4 blood test risks

The procedure for the T4 blood test is similar to other blood tests you may have had done. A technician will draw your blood with a small needle, and then cover the area with a bandage.

The risks from having your blood drawn are slight, but they can include:

• Pain following the needle stick (for most people this is mild)
• Bruising, if blood leaks under your skin
• Infection, if the area isn't kept clean
• Dizziness or fainting
• Feeling a lump under your skin

Understanding T4 Blood Test Results

Normal T4 range

Normal range on the free T4 test vary by age, sex assigned at birth, and lab testing method, but in general, they are as follows:

• Children up to 5 years old: 0.8-2.8 nanograms per deciliter (ng/dL)
• Children 6-15 years old: 0.8-2.1 ng/dL
• Teens 16-17 years old assigned male at birth: 0.8-2.8 ng/dL
• Teens 16-17 years old assigned female at birth: 0.8-1.5 ng/dL
• Adults over 18 years old: 0.9-1.7 ng/dL

For adults who are pregnant, the normal range on the free T4 test varies by trimester:

• First trimester: 0.8-1.53 ng/dL
• Second and third trimester: 0.7-1.20 ng/dL

Normal ranges (also called reference ranges) may vary between labs. Reference ranges are also set from studying large populations of people, so your result could be outside of the reference range but still normal for you. Ask your doctor about what your test results mean for you and your medical situation.

Low T4 levels

A few different conditions can cause low levels on a free T4 test, including:

• Hypothyroidism, which can be caused by not getting enough iodine in your diet. However, the main cause in most places where iodized salt is available is Hashimoto's thyroiditis , which is an autoimmune condition. An autoimmune condition is when your immune system mistakenly attacks your organs as if they were an invader, like a virus or bacteria.
• Untreated congenital (before you are born) hypothyroidism
• Severe short-term illness
• Malnutrition
• Some medicines, including such as amiodarone, dexamethasone, lithium, propranolol, and thionamide

High T4 levels

A few different conditions can cause high levels on a free T4 test, including:

• Too much iodine in your diet
• Benign (not cancer) tumor (thyroid adenoma) or nodules on your thyroid
• Graves' disease , an autoimmune condition
• Swelling of your thyroid (goiter)
• Taking too much thyroid replacement hormone
• Some tumors on the testes or ovaries (rare)
• Having medical imaging with a contrast dye that contains iodine (also rare)

Additional testing. While a free T4 test may show that there is a problem with your thyroid, it won't tell your doctor what the problem is. The next step is to figure out why your thyroid isn't working correctly. If your T4 levels aren't in a normal range, your doctor may order additional tests, such as:

TSH blood test. This is usually the first thyroid function test that your doctor will order, but if not, they may check it after your free T4 test comes back abnormal. Your TSH and T4 levels directly affect each other because TSH tells your thyroid when to make T4 and how much to make.

Free T3 blood test. Your doctor may want to check the levels of this other main hormone made by your thyroid gland.

Thyroid antibodies blood test. If you have a health condition like Hashimoto's thyroiditis or Graves' disease, your body may make proteins that attack your thyroid. If you're positive for thyroid antibodies , you may have one of these autoimmune conditions.

Radioactive iodine uptake imaging. Your thyroid needs iodine from your diet to make thyroid hormones. This test requires you to swallow a small amount of radioactive iodine. The technician will be able to see this iodine as it is being taken up into your thyroid using a special camera.

A T4 blood test measures your thyroxine hormone levels, which can show how well your thyroid is working. Low T4 levels are called hypothyroidism, and high T4 levels are called hyperthyroidism. Abnormal levels can be a short-term or long-term problem. Your doctor may order other thyroid function tests to help figure this out and decide on a treatment plan if you need one.

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Novosibirsk Oblast, Russia

The capital city of Novosibirsk oblast: Novosibirsk .

Novosibirsk Oblast - Overview

Novosibirsk Oblast is a federal subject of Russia, part of the Siberian Federal District. Novosibirsk is the capital city of the region.

The population of Novosibirsk Oblast is about 2,780,000 (2022), the area - 177,756 sq. km.

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History of Novosibirsk Oblast

Over thousands of years, the territory of the Novosibirsk region, due to its location on the border of natural zones and cultural regions (the Siberian taiga and the Eurasian steppe), played the role of a buffer zone or border zone of different peoples.

In the 13th-15th centuries, this land was the eastern outskirts of the Golden Horde. Later, until the end of the 16th century, it was part of the Siberian Khanate. In the 18th century, the territory of the present Novosibirsk region became part of the Russian Empire.

Despite the relatively favorable climate, the Russians began to settle here relatively late. The Barabin Tatars were the indigenous people. Today, their total population is about 10,000 people living mainly in the western parts of the region.

The Barabin Tatars were subjected to constant attacks of the Kalmyks (the Oyrates and Teleuts). Russian villages were also under the threat. That’s why people preferred to settle in the north, near Tomsk. Only at the end of the 17th century, Novosibirsk province became attractive to settlers.

More Historical Facts…

The first settlement was founded by the boyar son Alexey Kruglik in 1695. Later, this settlement became the village of Kruglikovo. Today, it is located in Bolotninsky district. In the early 18th century, Berdsky stockaded town was built. Over time, the threat from the nomads decreased and the number of settlers increased.

In 1722, the Siberian line of fortresses along the Irtysh River was constructed. The locals were mainly engaged in soil tilling, fishing and hunting. In the early 19th century, the famous Ural manufacturer Akinfiy Demidov constructed two copper melting plants here - Kolyvansky and Barnaulsky.

In 1893, due to the construction of the Trans-Siberian Railway and the railway bridge across the Ob River, Alexandrovsky settlement was built (from 1895 - Novonikolayevsky). Thanks to its convenient geographical location (the Trans-Siberian Railway crossing the Ob River, transportation ways connecting Siberia with the European part of the Russian Empire), its trade importance grew rapidly. In 1909, Novonikolayevsk became a town. In 1925, it was renamed in Novosibirsk.

Before 1921, the territory of Novosibirsk oblast was part of Tomsk gubernia, from 1921 to 1925 - of Novonikolayevsk gubernia, from 1925 to 1930 - of Siberian krai, from 1930 to 1937 - of West Siberian krai. September 28, 1937, West Siberian krai was divided into Novosibirsk oblast and Altay krai. This date is considered the official date of the region formation.

Novosibirsk Oblast - Features

Novosibirsk Oblast is located in the south east of the East-Siberian Plain, in the steppe, forest-steppe and taiga zones, between the Ob and the Irtysh rivers. The length of the region from west to east - 642 km, from north to south - 444 km.

The southern part of Vasyugan swamp, the largest swamp in the world, occupies the territory in the north and north-west of the province. In the southwest, it borders with Pavlodar oblast of Kazakhstan.

There are about 3,000 lakes on the territory of the Novosibirsk region. The largest lakes are Chany, Ubinskoye, Sartlan. Novosibirsk Reservoir also known as “the Ob Sea” (1,082 sq. km.) was created for Novosibirsk Hydroelectric Power Plant.

The climate is continental. The average temperature in January ranges from minus 16 degrees Celsius in the south and minus 20 degrees Celsius in the north. The average temperature in July - plus 18-20 degrees Celsius.

The largest cities and towns are Novosibirsk (1,621,000), Berdsk (103,500), Iskitim (54,700), Kuybishev (43,000). Novosibirsk is one the largest industrial, transport, scientific, and cultural center of Russia, the third most populous city in the country after Moscow and St. Petersburg. It is also the capital of the Siberian Federal District.

In the historical part of Novosibirsk you can find a lot of preserved monuments of the Russian Empire times. The Soviet era is presented by numerous scientific and cultural attractions, as well as beautiful parks.

There are more than 500 deposits of various mineral resources in Novosibirsk Oblast (coal, refractory clay, peat, anthracite). Natural gas and oil fields are located in the north-western part of the region. There are significant reserves of underground thermal and mineral waters. Forests cover about 4 million hectares, more than 20% of the territory.

Novosibirsk Oblast is one of the most industrially developed regions in Siberia (metal processing and machine building, food, power engineering, non-ferrous metallurgy industries). Heavy industries are concentrated in Novosibirsk, Iskitim and Berdsk.

The regional agriculture specializes in the cultivation of grain, potatoes and vegetables. Dairy cattle breeding, poultry farming and beekeeping are developed. The production of flax plays an important role too. Agricultural development of the territory is not high (about 48%). In general, it has about 25% of all agricultural land in Western Siberia.

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Learn more about the map styles

Each map type offers different information and each map style is designed for a different purpose. Read about the styles and map projection used in the above map (Physical Map of Novosibirsk).

Physical map

Physical map illustrates the mountains, lowlands, oceans, lakes and rivers and other physical landscape features of Novosibirsk. Differences in land elevations relative to the sea level are represented by color.

Green color represents lower elevations, orange or brown indicate higher elevations, shades of grey are used for the highest mountain ranges in the world. Underwater topography is represented by blues. Darker blues are used for the deepest water, lighter shades of blue represent shallower water such as the continental shelf.

Geographic map projection

A map projection is a way how to transform points on a Earth to points on a map. This map of Novosibirsk uses Plate Carree projection. The Plate Carree projection is a simple cylindrical projection originated in the ancient times. It has straight and equally spaced meridians and parallels that meet at right angles.

All projections from a sphere to a plane are distorted. The drawback of the Plate Carree projection is that it doesn't make an attempt to compensate for these distortions. For the general view of Novosibirsk, this is not a significant problem. The detailed maps use the Mercator projection which preserves the shape of small areas better.

Locations near Novosibirsk

Destinations close to Novosibirsk sorted by distance.

• Zaton 4.7 km
• Bol'shaya Krivoshchëkova 7.2 km
• Kar'yer 8.0 km
• Bugry 8.3 km
• Kar'yer Mochishche 8.5 km
• Ust'-Inya 8.8 km
• Levoberezhniy 9.8 km
• Ozërnyy 10 km
• Kamenka 10 km
• Katkovo 11 km

Popular searches

A list of the most popular locations in Russia as searched by our visitors.

• Yenisei River
• Krasnoyarsk
• Ural Mountains
• Kabardino-Balkarian Republic
• Kaliningrad Oblast
• Tomsk Oblast
• Lake Baikal

Recent searches

List of the locations in Russia that our users recently searched for.

• Kursk Oblast
• Udskaya Guba
• Amur Oblast
• Bagaevskaya
• Pskov Oblast

The Maphill difference

It's neither this physical map nor any other of the many millions of maps. The value of a map gallery is not determined by the number of pictures, but by the possibility to see the world from many different perspectives.

We unlock the value hidden in the geographic data. Thanks to automating the complex process of turning data into map graphics, we are able to create maps in higher quality, faster and cheaper than was possible before.

Forever free

We created Maphill to make the web a more beautiful place. Without you having to pay for it. Maphill maps are and will always be available for free.

Real Earth data

Do you think the maps are too beautiful not to be painted? No, this is not art. All 2D maps of Novosibirsk are created based on real Earth data. This is how the world looks like.

Easy to use

This map is available in a common image format. You can copy, print or embed the map very easily. Just like any other image.

Different perspectives

The value of Maphill lies in the possibility to look at the same area from several perspectives. Maphill presents the map of Novosibirsk in a wide variety of map types and styles.

Vector quality

We build each map individually with regard to the characteristics of the map area and the chosen graphic style. Maps are assembled and kept in a high resolution vector format throughout the entire process of their creation.

Experience of discovering

Maphill maps will never be as detailed as Google maps or as precise as designed by professional cartographers. Our goal is different. We want to redefine the experience of discovering the world through the maps.

Fast anywhere

Maps are served from a large number of servers spread all over the world. Globally distributed map delivery network ensures low latency and fast loading times, no matter where on Earth you happen to be.

Spread the beauty

Embed the above physical map of Novosibirsk into your website. Enrich your blog with quality map graphics. Make the web a more beautiful place.

Maphill is the web's largest map gallery.

Get a free map for your website. Explore the world. Discover the beauty hidden in the maps.

Map graphics revolution.™

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What Is a Free Thyroxine Test?

What to expect when undergoing this test

Purpose of Test

Risks and contraindications, before the test, interpreting results, a word from verywell.

A free thyroxine test, often called a free T4 test, measures the amount of free thyroxine in your blood. Thyroxine (also called T4) is one of the major hormones produced by your thyroid. When T4 is created, some of the hormone gets bound to proteins, while the rest circulates freely.

The free T4 that is being tested for is unbound and is available to the cells in the body to be used for things like heart and digestive function, metabolism, brain development, and bone and muscle health.

A healthcare provider may order a free T4 test if a patient is having symptoms of a thyroid disease , such as weight loss, a rapid heart rate, and sweating associated with hyperthyroidism (when your thyroid produces too many hormones). A free T4 test may also be performed if you are experiencing weight gain, feeling cold, or have a sense of general fatigue that might be associated with hypothyroidism (when the thyroid isn’t producing enough hormones).

Even if you aren’t showing any signs or symptoms of thyroid disease, your healthcare provider may want to run a free T4 test if you have a family history of thyroid conditions. A free T4 test is considered the most accurate test for assessing T4, as opposed to a total T4 test.

There are similar tests used to evaluate thyroid function, including a thyroid stimulating hormone (TSH) test and a triiodothyronine (T3) test. TSH is the hormone produced by the pituitary gland that informs the thyroid how much T4 and T3 hormones to produce in the body.

A T3 test may also be done alongside a free T4 test to help inform a diagnosis, as the measurement of free T4 together with T3 may be useful in identifying hyperthyroidism.

Since a T4 test is done simply with a blood draw, there are few to no risks of the procedure, aside from the risks you may have when getting blood drawn . You may have a headache or feel slightly queasy during the draw and notice tenderness, redness, or slight bruising at the site where the draw took place. If you feel nervous about having blood taken, make sure to tell the technician before they start the test so they can be aware and help make you feel more comfortable during and after the test.

For example, a small snack and drink after the blood draw may help with lightheadedness and any anxiety you may have that is associated with needles.

There are no preparations that need to be done ahead of time with a free T4 test, but you do need to tell your healthcare provider about any medications, vitamins, or herbs you are taking ahead of time, as these can interfere with the results of the test. Most healthcare providers will recommend having your blood drawn before you take any medications, if possible.

If you’re suffering from an illness such as a cold, your healthcare provider may also choose to postpone the blood draw until you’ve recovered. The test itself should only take a few minutes, and the results should be available a few days after your healthcare provider sends your blood vial off to the lab to be examined.

A free T4 test will likely take place right in your healthcare provider’s office. In certain cases, you may have to go to a separate lab to get your blood drawn at a time that is convenient for you.

What to Wear

Remember to wear a shirt that can be easily rolled up, or a sweatshirt with a t-shirt underneath so that you can remove it for the blood draw. It’s important for the technician performing the blood draw to be able to access your arm to find the best vein from which to take blood with minimal discomfort to you.

Food and Drink

Unless specified by your healthcare provider, hold off on any vitamins or medications until after your free T4 test. Supplements containing biotin should be ceased four days before the test. Make sure you eat a healthy meal or snack an hour or two before your free T4 test to prevent getting dizzy or lightheaded during the blood draw.

Cost and Health Insurance

When medically necessary, a free T4 test is usually covered by health insurance. Depending on your plan coverage, you may have to pay a coinsurance fee, which is usually anywhere from 10% to 50%.

Once your healthcare provider sends the blood draw off to the lab for analysis, the results should take no more than a few days to a week to come in. The results of a free T4 test vary depending on your age, gender, and health history. A normal free T4 range in adults is .8 to about 1.8 nanograms per deciliter (ng/dL). Higher T4 levels could indicate you have an overactive thyroid, while lower T4 levels could indicate you have an underactive thyroid.

Results from a free T4 test will help your healthcare provider determine the next set of tests to run as well as a treatment course, if necessary.

The results can also help show if the current prescribed treatment course for a previously diagnosed thyroid disease is working successfully. Free T4 tests are typically evaluated with other diagnostic thyroid tests, including a TSH test and sometimes a T3 test. For example, if the results show a high TSH level and a low free T4 level, this indicates hypothyroidism due to a defect in the thyroid.

A low TSH level and a low free T4 level is likely hypothyroidism due to a defect in the pituitary gland, and a low TSH level with a high free T4 level can be hyperthyroidism due to a defect in the thyroid.

While there are no lifestyle changes that can increase or decrease free T4 in the body, medication can be prescribed to help adjust the amount entering the bloodstream and ensure your body is operating with optimal levels of the hormone. In certain circumstances, such as pregnancy, free T4 levels may increase but are not necessarily a sign of thyroid disease. In cases like these, free T4 levels return to normal after the birth.

Reading free T4 test results alone without a comprehensive thyroid panel, including a TSH test, can give you an incomplete look into your thyroid function. This is because even if you see abnormal free T4 levels, it’s important to understand why those levels are abnormal, whether it’s an issue with your thyroid or with your pituitary gland.

Results of a free T4 test are just a glimpse of how your thyroid is functioning overall. As a result, it’s important to discuss all of the test results with your healthcare provider so they can determine what a normal T4 level and range for your health history is. Together, you can treat your specific thyroid disorder effectively with minimal side effects. 

Harvard Health Publishing. Thyroid hormone: How it affects your heart .

Carvalho GA, Perez CL, Ward LS. The clinical use of thyroid function tests . Arq Bras Endocrinol Metabol . 2013;57(3):193-204. doi:10.1590/S0004-27302013000300005 

Soh SB, Aw TC. Laboratory testing in thyroid conditions - pitfalls and clinical utility .  Ann Lab Med . 2019;39(1):3-14. doi:10.3343/alm.2019.39.1.3

Gupta S, Kaiti R, Gupta G. Evaluation of the female patients with subclinical hypothyroidism by brainstem auditory evoked potentials: Case-control study .  J Clin Diagn Res . 2017;11(6):CC13-CC16. doi:10.7860/JCDR/2017/25604.9989

American Thyroid Association. Thyroid function tests .

Blood Test: T4 (Thyroxine ). Kids Health From Nemours website.

Thyroxine (T4) Test . U.S. National Library of Medicine Medline Plus website.

Thyroid Function Tests . American Thyroid Association website.

Free T4 . University of Rochester Medical Center website.

By Colleen Travers Travers is a freelance writer and editor specializing in health, wellness, and fitness based in New York City.