Thyroid Stimulating Hormone Test

The function of the thyroid gland is to take iodine, found in many foods, and convert it into thyroid hormones: thyroxine (T4) and triiodothyronine (T3).

A thyroid stimulating hormone (TSH) blood test is used to check for thyroid gland problems.

TSH is produced when the hypothalamus releases a substance called thyrotropin releasing hormone (TRH).
TRH then triggers the pituitary gland to release TSH.

TSH causes the thyroid gland to make two hormones
T3 : triiodothyronine
T4 : thyroxine

T3 and T4 help control your body's metabolism.

Triiodothyronine (T3) and thyroxine (T4) are needed for normal growth of the brain, especially during the first 3 years of life. A baby whose thyroid gland does not make enough thyroid hormone (congenital hypothyroidism) may, in severe cases, be mentally retarded. Older children also need thyroid hormones to grow and develop normally.

A test for thyroid stimulating hormone (TSH) is done to Find out whether the thyroid gland is working properly.
  • Hypothyroidism : - An underactive thyroid gland () can cause symptoms such as weight gain, tiredness, dry skin, constipation, a feeling of being too cold, or frequent menstrual periods. 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).
  • Hyperthyroidism : - An overactive thyroid can cause symptoms such as weight loss, rapid heart rate, nervousness, diarrhea, a feeling of being too hot, or irregular menstrual periods.

Preparation For TSH test
The TSH test doesn’t require any special preparation. However, it’s important to tell your doctor if you’re taking medications that might interfere with the accuracy of the TSH measurement. Your test results may not be correct if you have had iodine contrast material before having a thyroid-stimulating hormone (TSH) test. So tell your doctor if you have had any tests in which you were given radioactive materials or had X-rays that used iodine dye within the last 4 to 6 weeks. Some medications that could interfere with a TSH test are

Potassium iodide

You may need to avoid using these drugs before the test. However, don’t stop taking your medications unless your doctor tells you to do so.

TSH test Results

The normal values listed here called a reference range are just a guide. These ranges vary from lab to lab.

Results are usually available in 2 to 3 days.

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

Low TSH levels may be caused by
  1. 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.
  2. Damage to the pituitary gland that prevents it from making TSH (a condition called secondary hypothyroidism).
  3. Taking too much thyroid medicine for treatment of an underactive thyroid gland.
  4. Pregnancy during the first trimester.

High TSH levels may be caused by
  1. An underactive thyroid (hypothyroidism). Hashimoto's thyroiditis is the most common cause of primary hypothyroidism.
  2. A pituitary gland tumor that is making too much TSH. This is uncommon.
  3. Not taking enough thyroid hormone medicine for treatment of an underactive thyroid gland.


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