TSIDefinition: TSI is a test that measures the amount of TSI antibody in the blood.
Alternative Names: TSH receptor antibody; Thyroid stimulating immunoglobulin
How the test is performed: Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to fill with blood. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. The tourniquet is then removed to restore circulation. After blood has been collected the needle is removed, and the puncture site is covered to stop any bleeding. Infant or young child: The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.
How to prepare for the test: No special preparation is usually necessary.
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: This test may be performed as part of the diagnostic work-up of Graves' disease, Hashimoto's Thyroiditis, or toxic multinodular goiter. TSI measurements are also performed in the third trimester of pregnancy to predict neonatal Graves' disease. TSI is an antibody directed against the receptor for TSH on the thyroid gland. This antibody interacts with the receptor and mimics the action of the pituitary hormone TSH. Thus TSI stimulates the gland to secrete excessive amounts of thyroid hormone.
Normal Values: Normal values are less than 130% of basal activity. Normal value ranges may vary slightly among different laboratories.
What abnormal results mean: Greater-than-normal levels may indicate: - Graves' disease
- Hashitoxicosis
- Neonatal thyrotoxicosis
What the risks are: - Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
- Multiple punctures to locate veins
Special considerations: 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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