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    Thyroid-Stimulating Hormone (TSH)

    A thyroid-stimulating hormone (TSH) blood test is used to check for thyroid gland camera.gif problems. TSH is produced when the hypothalamus releases a substance called thyrotropin-releasing hormone (TRH). TRH then triggers the pituitary gland camera.gif to release TSH.

    TSH causes the thyroid gland to make two hormones: triiodothyronine (T3) and thyroxine (T4). 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.

    This test may be done at the same time as tests to measure T3 and T4.

    Why It Is Done

    A test for thyroid-stimulating hormone (TSH) is done to:

    • Find out whether the thyroid gland is working properly.
    • 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).
    • Keep track of treatment with thyroid replacement medicine for people who have hypothyroidism.
    • Keep track of 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).

    How To Prepare

    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. Your test results may not be correct if you have had iodine contrast material before having a thyroid-stimulating hormone (TSH) test.

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    WebMD Medical Reference from Healthwise

    Last Updated: November 14, 2014
    This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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