Thyroid Stimulating Hormone

Is a blood test used to check for thyroid gland problems.

TSH causes the thyroid gland to make two hormones: triiodothyronine (T3) and thyroxine (T4). T3 and T4 help control your body’s metabolism.

Why It Is Done

  • To determine if the thyroid gland is working properly. An underactive thyroid gland (hypothyroidism) can cause symptoms such as weight gain, tiredness, dry skin, constipation, a feeling of being too cold, or frequent menstrual periods. An overactive thyroid (hyperthyroidism) can cause symptoms such as weight loss, rapid heart rate, nervousness, diarrhea, a feeling of being too hot, or irregular menstrual periods.
  • Find the cause of an underactive thyroid gland (hypothyroidism). TSH levels can help determine whether hypothyroidism is due to a damaged thyroid gland or some other cause (such as a problem with the pituitary gland or the hypothalamus).
  • To keep track of treatment with thyroid replacement medicine for people who have hypothyroidism.
  • To monitor the thyroid gland function in people who are being treated for hyperthyroidism. This treatment may include antithyroid medicine, surgery, or radiation therapy.
  • Double-check the diagnosis of an underactive thyroid gland in a newborn (congenital hypothyroidism).
  • Diagnose and monitor female infertility problems.

What are the normal values for TSH?

The normal values listed here—called a reference range—vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses.

Results are usually available on the same day. There is no preparation required for this test.

Thyroid-stimulating hormone (TSH)

Adults:0.4–4.2 microunits per milliliter (mcU/mL) or 0.4–4.2 milliunits per liter (mU/L)

Children: 0.7–6.4 mcU/mL or 0.7–6.4 mU/L

Newborns ( 1-4 days): 1–39 mcU/mL or 1–39 mU/L

A slightly high TSH value may not require treatment. The doctor will consider any symptoms you might have along with other test results to determine if treatment is needed.

High TSH levels may be caused by:

  • An underactive thyroid (hypothyroidism). Hashimoto’s thyroiditis is the most common cause of primary hypothyroidism.
  • A pituitary gland tumor that is making too much TSH. This is uncommon.
  • Not taking enough thyroid hormone medicine for treatment of an underactive thyroid gland.

Low TSH levels may be caused by:

  • An overactive thyroid gland (hyperthyroidism). Causes of hyperthyroidism include Graves’ disease, a type of goiter (toxic multinodular goiter), or a noncancerous (benign) tumor called a toxic nodule.
  • Damage to the pituitary gland that prevents it from making TSH (a condition called secondary hypothyroidism).
  • Taking too much thyroid medicine for treatment of an underactive thyroid gland.
  • Pregnancy during the first trimester.

Some more information about the TSH test……

  • The thyroid-stimulating hormone (TSH) test is the best screening test for conditions that can affect the thyroid gland.
  • The results of a TSH test should be considered along with the results of thyroid hormone tests, especially thyroxine (T4) results.
  • Many medications — including aspirin and thyroid-hormone replacement therapy — may affect thyroid gland function test results and their use should be discussed with the doctor prior to testing.
  • When a doctor adjusts a person’s thyroid hormone replacement dosage, it is important to wait at least one to two months before checking the TSH again so that the new dose can have its full effect.
  • Extreme stress and acute illness may also affect TSH test results, and results may be low during the first trimester of pregnancy.

What is a 3rd generation TSH and an ultrasensitive TSH?

Both of these terms relate to the evolution of the TSH test. Over time, increasingly sensitive and specific TSH tests have been developed and adopted. Most laboratories now use the 3rd generation/ultrasensitive TSH test as their “TSH test.” This newest version is about 100 times more sensitive than the first-generation TSH test.