Thyroid-Stimulating Hormone

The amount of thyroid-stimulating hormone (TSH) or thyrotropin can be measured from a sample of blood. The TSH level can help diagnose thyroid gland or pituitary gland disorders, or monitor treatment of hypothyroidism and hyperthyroidism. TSH is produced by the pituitary gland, a tiny organ located below the brain.

The pituitary gland is part of the body's feedback system to maintain stable levels of thyroid hormones released into the blood. Thyroid hormones help control the rate at which the body uses energy. The pituitary gland monitors the level of thyroid hormones released by the thyroid gland. The thyroid gland is a small butterfly-shaped gland that lies flat against the windpipe.

If the thyroid gland does not release enough thyroid hormones, the pituitary gland detects the reduced thyroid hormone levels. The pituitary gland then makes more TSH to trigger the thyroid gland to produce more thyroid hormones. This increase in TSH is an effort to return the low thyroid hormones to normal levels. The increased TSH level is caused by the low thyroid hormone levels of an underactive thyroid (hypothyroidism). Symptoms of hypothyroidism include menstrual irregularities in women, weight gain, dry skin, constipation, cold intolerance, and fatigue. Rarely, a high TSH level can indicate a problem with the pituitary gland. A high TSH level could also occur when there is an insufficient level of thyroid hormone medication in individuals receiving that medication.

If the thyroid gland releases too much thyroid hormones, the pituitary gland detects the increased thyroid hormone levels. The pituitary gland then makes less TSH to slow the thyroid gland from producing thyroid hormones. This decrease in TSH is an effort to return the increased thyroid hormones to normal levels. The decreased TSH level is caused by the excess thyroid hormone levels of an overactive thyroid gland (hyperthyroidism). Symptoms associated with hyperthyroidism include rapid heart rate, weight loss, nervousness, hand tremors, irritated eyes, and difficulty sleeping. Rarely, a low TSH level can indicate a problem with the pituitary gland.

PREPARATION FOR TEST

No specific preparation is required for this blood test. A blood sample is obtained from a needle placed in a vein in your arm or from pricking the heel of an infant.

NORMAL FINDINGS

  • Adult: 0.5-5 milli-international Units/L (0.5-5 mIU/L)

  • Newborn: 3-20 milli-international Units/L (3-20 mIU/L)

  • Cord: 3-12 milli-international Units/L (3-12 mIU/L)

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.

MEANING OF TEST

Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.

OBTAINING THE TEST RESULTS

It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.