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Alternative names Return to top
Thyrotropin; Thyroid stimulating hormoneDefinition Return to top
TSH is a test that measures the amount of the hormone TSH in the blood.How the test is performed Return to top
Adult or child:How to prepare for the test Return to top
No special preparation is usually necessary.
Infants and children:
The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:
How the test will feel Return to top
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.Why the test is performed Return to top
TSH is measured as a screening test for abnormal thyroid function.
TRH, a hormone produced in the hypothalamus, stimulates the pituitary gland to release TSH. TSH subsequently stimulates the thyroid to produce thyroid hormone, T3 and T4. These hormones feedback to the hypothalamus and pituitary to regulate the release of both TSH and TRH.
In certain diseases, this regulation pathway is altered leading to under- or over-production of thyroid hormone. When a thyroid disorder is suspected clinically, a TSH level is obtained as an initial test.
Normal Values Return to top
Normal values are from 0.4 to 4.0 mIU/L for those with no symptoms of an under- or over-active thyroid.
If you are being treated for a thyroid disorder, your TSH should be between 0.3 and 3.0 mIU/L. This means that you are being treated appropriately.
Some people with a TSH value over 2.5 mIU/L who have no signs (that is, no other abnormal thyroid function tests) or symptoms suggestive of an under-active thyroid may develop hypothyroidism sometime in the future. Anyone with a TSH above 2.5 mIU/L, therefore, should be followed very closely by a doctor.
Normal value ranges may vary slightly among different laboratories.
What abnormal results mean Return to top
Greater-than-normal levels may indicate:What the risks are Return to top
Special considerations Return to top
Drugs that can affect TSH measurements include: antithyroid medications, lithium, potassium iodide, amiodarone, dopamine and prednisone.
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
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Page last updated: 28 October 2004 |