A TSH test measures the amount of thyroid stimulating hormone (TSH) in your blood. TSH is produced by the pituitary gland and tells the thyroid gland to make and release the hormones thyroxine (T4) and triiodothyronine (T3).
T3 test T4 test
Thyrotropin; Thyroid stimulating hormone
How the test is performed
Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
How to prepare for the test
Your health care provider may ask you to stop taking drugs that may interfere with the test. Drugs that can affect TSH measurements include:
- Antithyroid medications
- Potassium iodide
How the test will feel
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
Your doctor will order this test if you have signs of abnormal thyroid function (
Review Date: 12/10/2010
Reviewed By: A.D.A.M. Editorial Team: David Zieve, MD, MHA, and David R. Eltz. Previously reviwed by Ari S. Eckman, MD, Division of Endocrinology and Metabolism, Johns Hopkins School of Medicine, Baltimore, MD. Review provided by VeriMed Healthcare Network (4/19/2010).