Thyroid Stimulating Hormone (TSH)

The thyroid gland is an endocrine gland. It has a shape of a butterfly, and is located in the lower front of the neck. The main function of the thyroid gland is to produce hormones – thyroxine (T4) and triiodothyronine (T3) – which are released into the bloodstream and then transferred to every cell in the body. These hormones help the body use energy, keep the muscles, heart, brain, and other organs functioning the right way.

What is TSH?

Thyroid-stimulating hormone (TSH) is produced by the pituitary gland (or rather by its anterior lobe – adenohypophysis), which is located at the base of the brain. TSH controls the work of the thyroid gland, namely, the production of its main hormones: thyroxine (T4) and triiodothyronine (T3). There is an inverse relationship between the concentration of TSH and the concentration of T4 in the blood. If the thyroid gland produces too little T4, then the level of TSH in the blood will increase. Conversely, if the amount of T4 is too high, the level of TSH will decrease.

Thyroid Stimulating Hormone (TSH)

Interpret now "Complete Blood Count (CBC)"
Interpret now "Comprehensive Metabolic Panel (CMP)"
Interpret now "Urinalysis (UA)"

However, if the pituitary is not working properly, it does not produce enough TSH. In this case, even if the thyroid gland is healthy, it does not receive enough TSH and therefore produces too little T4. Fortunately, such disorder is quite rare.

The TSH test is carried out in cases of suspected thyroid disease (chronic autoimmune thyroiditis, diffuse toxic goiter, postoperative hypothyroidism, nodular goiter) or pituitary disease. In the case of pituitary disease, an isolated increase in thyroid-stimulating hormone can be observed with normal thyroid hormone levels.

TSH is very sensitive to changes in thyroid hormone levels, so it is often used to screen for thyroid dysfunction.

TSH Normal Range

TSH can be measured in mIU/L (milli-international units per liter) or mU/L (milliunits per litre), μIU/mL (microunits per milliliter). All these units are equal for TSH (mIU/L = mU/L = μIU/mL). Some labs use different measurements.

TSH reference ranges according to
the Website of the American Thyroid Association® ( (mU/L)

Normal and abnormal TSH levels (mU/L)

According to a 2013 study, the reference range of TSH increases with age, while T4 free decreases. At the age of 60 to 79 years old, the normal level of TSH is 0.4-5.8 mIU/L, and from 80 years old and older TSH level is 0.4-6.7 mIU/L. The use of age-specific TSH reference intervals, especially in people over 70 years old, helps to avoid the erroneous diagnosis of subclinical hypothyroidism and unnecessary treatment.

The normal level of TSH indicates the normal functioning of the thyroid gland, but cannot exclude the presence of inflammatory diseases of the thyroid gland.

You must use the reference range of the laboratory that performed your test when trying to interpret the test results.

Normal TSH Levels in Pregnancy

Thyroid hormone is necessary for the normal development of the baby’s brain during pregnancy. During the first trimester, the child receives thyroid hormones from the mother. In the second trimester of pregnancy, the developing thyroid gland of the child begins to produce hormones on its own.

With an insufficient amount of thyroid hormones in the mother during pregnancy, the child may be born with a lower IQ level, compared with the normal functioning of the thyroid gland. But the child is not at increased risk for birth defects.

During pregnancy there is a decrease in both the lower limit of TSH reference range (decreases by about 0.1-0.2 mIU/L) and the upper limit (decreases by approximately 0.5-1.0 mIU/L), relative to the usual nonpregnant TSH reference range.

The largest decrease in the TSH level in the blood is observed in the first trimester of pregnancy due to the increasing chorionic gonadotropin (hCG). The hormone hCG causes an increase in thyroid hormone levels, thus suppressing TSH. Then gradually the level of TSH returns to normal levels. Since the concentration of hCG in multiple pregnancies is higher, the TSH level decreases more than during singleton pregnancies.

Normal TSH Levels in Children

According to a study that measured the TSH level in children from birth to 18 years of age, the level of thyroid stimulating hormone varies greatly depending on the age of the child.

For full-term newborns, the range of normal levels of TSH is quite large and can be 0.7-16 mIU/L. The TSH level in the blood gradually decreases, approaching adult values, while free thyroxin (T4 free) will remain relatively stable over the same time period.

Elevated TSH Levels (Hypothyroidism)

Hypothyroidism is one of the most common diseases of the thyroid gland. In hypothyroidism, the thyroid gland produces an insufficient amount of hormones, which leads to a slower metabolism. Hypothyroidism can develop at any age, but the risk of its development increases with age.

Thyroid function disorders can cause a number of health problems, such as heart disease, obesity, infertility, and joint pain.

A research studies the prevalence of thyroid dysfunction and depression in people with central (abdominal) obesity. Participants with central obesity had a higher prevalence of hypothyroidism and depression than non-obese controls. Free T4 and TSH are important for weight control. Depression is positively correlated with obesity.

Subclinical hypothyroidism

Subclinical hypothyroidism is a condition in which the level of thyroid-stimulating hormone (TSH) is above normal, while the level of thyroxin (T4) and triiodothyronine (T3) remains within the reference values. Subclinical hypothyroidism is usually asymptomatic, so the diagnosis is made according to the results of a blood test when the TSH level exceeds 4.0 mIU/L. According to studies, the onset of symptoms and complications is more common in patients whose TSH level exceeds 10.0 mIU/L. Therefore, replacement therapy is recommended to start at a TSH level above 10.0 mIU/L. Further research is needed to find out how subclinical hypothyroidism affects health and whether it needs to be treated. If TSH values are less than 10.0 mIU/L, substitution therapy should be considered if there are general symptoms, antibodies to the thyroid gland, elevated lipids and other risk factors, as well as goiter, ovarian dysfunction, infertility, and pregnancy.

Symptoms of hypothyroidism

Hypothyroidism does not cause any unique symptoms. It may develop slowly over several years, and as a result the symptoms may be less noticeable or ignored. The lower the level of thyroid hormones, the harder the symptoms will be. Subclinical hypothyroidism can cause mild symptoms or has no symptoms at all, while severe hypothyroidism usually causes severe symptoms.

The main symptoms of hypothyroidism include:

  • weakness, fatigue, drowsiness
  • hypersensitivity to cold
  • dry skin, brittle hair and nails
  • loss of appetite
  • weight gain and difficulty losing weight
  • memory problems
  • depression, irritability
  • irregular periods
  • muscle cramps and joint pain
  • enlargement of the thyroid gland (goiter)

Since symptoms do not always appear, a blood test for thyroid hormones should be done to confirm the diagnosis.

Hypothyroidism in children

Hypothyroidism in children may be congenital or may develop later (acquired hypothyroidism). In general, in children and adolescents, the symptoms are the same as in adults. In addition, children may experience other important symptoms:

  • slow growth
  • delayed sexual development
  • delayed development of permanent teeth
  • poor mental development

In many children, subclinical hypothyroidism resolves without treatment, and the function of the thyroid gland returns to normal.

Hypothyroidism Treatment

Hypothyroidism treatment should be carried out under medical supervision. There is no cure for hypothyroidism. The goal of the treatment is to replicate normal thyroid functioning.

Chinese herbs, selenium, dietary supplements with iodine, seaweed and other herbal remedies that are high in iodine cannot cure hypothyroidism. When the thyroid gland is not working properly, taking additional iodine will not help it work better. Too much iodine in the body can worsen both hypothyroidism and hyperthyroidism.

Low TSH levels (hyperthyroidism, thyrotoxicosis)

Hyperthyroidism is a condition characterized by the overproduction of thyroid hormones thyroxine (T4) and triiodothyronine (T3) by the thyroid gland. Thyrotoxicosis is a condition when too much thyroid hormone of any cause is present in the body and therefore includes hyperthyroidism.

In hyperthyroidism, it is necessary to control the amount of thyroid hormones in the body, because often people who are treated for hyperthyroidism eventually develop hypothyroidism. But in hypothyroidism, hormone deficiency is easily compensated by medication, while without treatment, hyperthyroidism causes serious health problems.

Subclinical hyperthyroidism

In subclinical hyperthyroidism, the thyroid gland produces normal amounts of the hormones T4 and T3, but at the same time, the level of thyroid stimulating hormone (TSH) is below normal. The need for treatment of subclinical hyperthyroidism remains questionable and is solved individually. In subclinical hyperthyroidism, low TSH levels return to normal values on their own in nearly 50 percent of people.

Symptoms of hyperthyroidism (thyrotoxicosis)

Hyperthyroidism accelerates metabolism. The more hormones T3 and T4 are in the blood, the faster the metabolism. Symptoms are often mistaken for stress or other health problems. They may include:

  • nervousness
  • tiredness
  • weight loss
  • raised blood pressure
  • a rapid pulse
  • menstrual disorders
  • increased sweating
  • hair loss
  • frequent bowel movements

Hyperthyroidism Causes

The most common cause of hyperthyroidism is Graves' disease. This is an autoimmune disorder in which immune system attacks the thyroid gland and causes it to grow and produce too many hormones. Graves disease occurs more often in young women.

Hyperthyroidism can also be caused by thyroid nodules, which produce an increased amount of hormones.

Other causes of hyperthyroidism:

  • Thyroiditis – an inflammation of the thyroid gland, due to which too many hormones are secreted into the blood. Over time, thyroiditis leads to hypothyroidism.
  • Increased iodine intake can lead to hyperactivity of the thyroid gland. This can happen as a result of regular use of certain medications that contain iodine (for example, amiodarone.)
  • Taking too much thyroid hormone replacement medication.

Hyperthyroidism in children

Hyperthyroidism in children is less common than in adults. It is often difficult for parents to distinguish symptoms of hyperthyroidism from other physical and emotional problems. Children are often diagnosed with ADD or ADHD. This diagnosis can be excluded by a blood test, which shows a high level of thyroid hormones and a low level of thyroid stimulating hormone (TSH).

In general, in children and adolescents, the symptoms are the same as in adults, but they may also experience poor performance at school, difficulties with concentration, fatigue, difficulty falling asleep.

Hyperthyroidism Treatment

The goals of treatment for hyperthyroidism are to return thyroid hormone levels to normal range, prevent health problems that can be caused by hyperthyroidism, and get rid of unpleasant symptoms. The choice of treatment depends on the age, the cause of hyperthyroidism, the severity of hyperthyroidism, general health and other disorders that may affect treatment. There are several ways to treat hyperthyroidism:

  • Antithyroid medications that suppress the activity of the thyroid gland.
  • Radioactive iodine therapy. It involves taking a capsule with radioactive iodine. Radioactive iodine enters the bloodstream and is absorbed by the thyroid gland, which leads to the destruction of its cells. Hypothyroidism often develops after treatment. This method has been used for over 60 years and is a safe and effective treatment.
  • Surgery. All or part of the thyroid gland is removed. In most cases, hypothyroidism develops.

  • Thyroid Function Tests. (n.d.)
  • Fontes, R., Coeli, C.R., Aguiar, F. et al. “Reference interval of thyroid stimulating hormone and free thyroxine in a reference population over 60 years old and in very old subjects (over 80 years): comparison to young subjects.” Thyroid Res 6, 13 (2013).
  • Erik K. Alexander, Elizabeth N. Pearce, Gregory A. Brent et al. “2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum.” Thyroid. Mar 2017.315-389.
  • Kapelari, Klaus et al. “Pediatric reference intervals for thyroid hormone levels from birth to adulthood: a retrospective study.” BMC endocrine disorders vol. 8 15. 27 Nov. 2008
  • Du, Fu-Man et al. “Effects of thyroid hormone and depression on common components of central obesity.” The Journal of international medical research vol. 47,7 (2019): 3040-3049.
  • Santos Palacios, Silvia et al. “Management of subclinical hyperthyroidism.” International journal of endocrinology and metabolism vol. 10,2 (2012): 490-6.
  • Patil N, Rehman A, Jialal I. Hypothyroidism. [Updated 2020 Feb 20]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from:
Thyroid Function Tests (TFTs) Interpretation