Thyroid Stimulating Hormone (TSH) Test – Everything You Need to Know

The TSH test is a measure of the amount of Thyroid Stimulating Hormone (TSH) in the body. TSH is a pituitary hormone that controls the production of the hormones that are necessary for tissue metabolism in the body. In this post, we will learn all about the TSH test and the need to track it for optimum body performance.

What is the thyroid?

The thyroid is one of the most important glands in our body. It is situated low on the front of the neck and produces 2 thyroid hormones (TH): thyroxine (usually referred to as T3) and triiodothyronine (T4). Both of these hormones are essential for maintaining good metabolism, brain development, heart and digestive health, as well as good muscle and bone health1.

In addition, the thyroid gland produces calcitonin, a protein-based hormone that protects the body from elevated blood calcium levels, a condition known as hypercalcemia2.

What is Thyroid Stimulating hormone?

Thyroid-stimulating hormone, or TSH, is released by the pituitary gland (a tiny organ below the brain) into the bloodstream. The pituitary gland releases TSH in response to low levels of thyroid hormones, as it stimulates their production in the thyroid. TSH is a part of a feedback loop; once thyroid hormone levels are sufficiently high, the body will signal to the pituitary gland to stop producing TSH, preventing the TH levels from becoming too high3.

Therefore, TSH levels are a direct reflection of T3 and T4 release from the thyroid, which in turn control many important processes in the body. By measuring TSH levels, we can identify underlying thyroid problems.

What does the Thyroid Stimulating Test measure?

The TSH test directly measures the level of TSH in your bloodstream. If all the organs in the TH-releasing system are working correctly, this remains constantly within the normal range. However, if the pituitary gland or the thyroid stops functioning normally, this can throw off the balance of TSH in the blood. This can be caused by several issues, although the most common are hypothyroidism and hyperthyroidism.

What is hypothyroidism?

Hypothyroidism is a condition that occurs when the thyroid gland does not produce enough thyroid hormones. A doctor can usually diagnose this by looking at TSH levels, which are elevated in hypothyroidism. This is because the pituitary gland detects low TH levels, so in response, it releases more TSH to stimulate TH production.

People with hypothyroidism usually suffer from the following symptoms:

  • Weight gain
  • Fatigue
  • Difficulty concentrating
  • Depression
  • Irregular periods

Patients with hypothyroidism are most commonly treated with levothyroxine, a hormone that replaces T3. If left untreated, hypothyroidism increases the risk of heart disease and reduces life expectancy.

The most common cause of serious hypothyroidism is Hashimoto’s disease, an autoimmune disorder where the body produces special antibodies that destroy cells in the thyroid gland and therefore decrease the release of thyroid hormones4.

What is hyperthyroidism?

Hyperthyroidism is a less common condition where levels of thyroid hormones are too high. This can be diagnosed by testing for TSH, which is abnormally low in patients with hyperthyroidism. This is because the pituitary gland detects high TH levels, so it stops producing TSH as it no longer needs to stimulate TH production.

Hyperthyroidism causes many of the processes in the body to speed up, including our metabolism, which can lead to unexplained weight loss. Some of the other symptoms of hyperthyroidism include5:

  • Fatigue
  • Excessive sweating and inability to tolerate heat
  • Fast heart rate and palpitations
  • Irregular sleep
  • Anxiety

Usually, hyperthyroidism is treated using antithyroid drugs, which reduce the production of T3 and T4 in the thyroid6. If left untreated, hyperthyroidism can lead to heart failure.

The most common cause of serious hyperthyroidism is Graves’ disease, an autoimmune disorder that causes the production of an antibody that mimics TSH, and therefore stimulates the thyroid to produce high levels of thyroid hormones5,7.

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When should you test your TSH levels?

Usually, your doctor will order a TSH test if you have symptoms of hypo- or hyperthyroidism. In addition, it can also be used to monitor how well a treatment is working in patients with already diagnosed hypo- or hyperthyroidism8.

Other uses of the test include:

  • Investigating infertility in women
  • Testing function of the pituitary gland
  • Monitoring cancer patients who have had thyroid tissue removed

Nevertheless, routine testing of TSH can also be beneficial to our health. This is because patients and medical professionals rarely make the connection between symptoms such as changes in weight and depression with thyroid dysfunction. In addition, thyroid problems can be symptomless for long periods of time. As a result, many people remain undiagnosed for several years, and only begin treatment at later and more resistant stages of the disease.

What are the optimal levels on a TSH test?

Most labs state that the ‘normal’ reference range for TSH is 0.27 and 4.3 mIU/L.

However, several studies have found that the upper limit of this range may be too high. In fact, many researchers have suggested that the upper limit should actually be as low as 2.5 mIU/L9.

TSH test - reference range
TSH test – Reference Range (mlU/L)
TSH test – Optimal Range (mlU/L)

To understand why reference ranges may be misleading, we must first understand how optimal ranges are calculated. Labs take the results of a large number of tests and identify the range that 95% of these results fall into. This method provides an accurate estimation of a ‘healthy’ range for some blood tests, but for many, it falls short.

In the case of TSH tests, reference ranges are insufficient because individuals with undiagnosed thyroid dysfunction can skew the distribution of test results.

This, unfortunately, represents a large proportion of the population, as thyroid dysfunction is famously underdiagnosed. This means that the reference ‘normal’ ranges are not representative of good long-term thyroid health, as the sample from which they are calculated is not healthy in itself.

The skewed data means that often, being within the normal TSH range can give you a false sense of security when there are issues with your results that you could be addressing in order to optimise your health.

At ElevateMe, we use optimal ranges instead of reference ranges for all our analyses. This ensures that your blood test results are in reference to the healthiest of individuals. You can learn more about optimal ranges in blood tests here.

What does a high level of TSH mean?

A high level of TSH can be an indicator of hypothyroidism. Sometimes, pituitary gland issues such as a tumour can be the cause of extremely high TSH levels8.

What does a low level of TSH mean?

A lower level of TSH can indicate that you may be suffering from clinical or pre-clinical hyperthyroidism. In rare cases, it can also indicate damage to the pituitary gland that prevents it from producing sufficient TSH. If you are already receiving thyroid hormone medication, low TSH could mean that your dosage is too high. You should speak to your doctor if you are concerned about your TSH results8.

How is the TSH test performed?

In a clinic, the test is done by taking a blood sample from a vein. You can also complete the TSH test with an at-home finger prick blood test. There is no preparation needed, so you do not need to fast before the test.

Some types of medication can interfere with the accuracy of a TSH test. This includes thyroid hormone replacement therapy, lithium, and amiodarone. If your TSH results are not optimal, it is best to let your doctor know about any medication that you are taking before getting advice8.

How does pregnancy affect TSH?

Researchers have noticed that pregnant women, especially in the first trimester, have abnormally low TSH levels. This is because the baby cannot produce its own thyroid hormones, which are necessary for development, and therefore relies on the mother to provide T4.

If untreated, hypothyroidism during pregnancy can increase the risk of miscarriage, premature birth and other pregnancy complications. Because of this, many pregnant women take levothyroxine to improve their thyroid hormone levels. If you are pregnant, you should speak to your doctor about optimising your TSH levels10.

Are there people more at risk for abnormal thyroid-stimulating hormone levels?

Some groups have a higher prevalence of thyroid dysfunction. For example, women and older people are more likely to suffer from both hypo- and hyperthyroidism11. In addition, a family history of thyroid problems can mean that you are more likely to have thyroid dysfunction.


Because thyroid dysfunction is notoriously underdiagnosed, it is important to regularly monitor your TSH levels to ensure that you catch any problems and start treatment early. Especially if you are in one of the risk groups.

This is why the ElevateMe program, which offers a TSH test with research-based optimal ranges, recommends that you repeat blood tests regularly. Our health plans include re-testing every 3, 6, or 12 months, depending on your goals. At this timescale, you will be able to monitor any changes or irregularities in your TSH levels and seek medical advice when needed.

Join ElevateMe today and take steps towards gaining control over your long-term health and feeling your best every day.

Are you tired? 

Thyroid disease is known to cause lethargy, muscle weakness, and irritability12. Up to 60% of people with thyroid disease are unaware of having it13.  

Take an ElevateMe blood test today to capture your TSH levels and 20 other blood test insights to track your sleep, fitness, energy, metabolism, cognition, mood, and immunity.

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  1. Chi, H.C., Chen, C.-Y., Tsai, M.-M., Tsai, C.-Y. and Lin, K.-H. (2013). Molecular Functions of Thyroid Hormones and Their Clinical Significance in Liver-Related Diseases. BioMed Research International, 2013, pp.1–16.
  2. Felsenfeld, A.J. and Levine, B.S. (2015). Calcitonin, the forgotten hormone: does it deserve to be forgotten? Clinical Kidney Journal, 8(2), pp.180–187.
  3. Fitzgerald, S.P. and Bean, N.G. (2018). Thyroid stimulating hormone (TSH) autoregulation reduces variation in the TSH response to thyroid hormones. Temperature, 5(4), pp.380–389.
  4. Chiovato, L., Magri, F. and Carlé, A. (2019). Hypothyroidism in Context: Where We’ve Been and Where We’re Going. Advances in Therapy,36(S2), pp.47–58.
  5. Igor Kravets (2016). Hyperthyroidism: Diagnosis and Treatment. American Family Physician, 93(5), pp.363–370.
  6. De Leo, S., Lee, S.Y. and Braverman, L.E. (2016). Hyperthyroidism. The Lancet, 388(10047), pp.906–918.
  7. Labtestsonline.org. (2019). Graves Disease
  8. Labtestsonline.org.uk. (2019). TSH.
  9. Biondi, B. (2013). The Normal TSH Reference Range: What Has Changed in the Last Decade? The Journal of Clinical Endocrinology & Metabolism, 98(9), pp.3584–3587.
  10. Taylor, P.N., Minassian, C., Rehman, A., Iqbal, A., Draman, M.S., Hamilton, W., Dunlop, D., Robinson, A., Vaidya, B., Lazarus, J.H., Thomas, S., Dayan, C.M. and Okosieme, O.E. (2014). TSH Levels and Risk of Miscarriage in Women on Long-Term Levothyroxine: A Community-Based Study. The Journal of Clinical Endocrinology & Metabolism, 99(10), pp.3895–3902.
  11. Chaker, L., Bianco, A.C., Jonklaas, J. and Peeters, R.P. (2017). Hypothyroidism. The Lancet, 390(10101), pp.1550–1562.
  12. Website [Internet]. [cited 2021 Jul 08] Available from:https://www.thyroid.org/hypothyroidism/
  13. Website [Internet]. [cited 2021 Jul 08] Available from:https://www.thyroid.org/media-main/press-room/

TSH test doctor checking thyroid

Written by Natalia Glazman

I'm a Biochemistry student at Imperial College, interested in all things immunology and pursuing a career in science communication.


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