TSI stands for thyroid stimulating immunoglobulin. TSIs are antibodies that tell the thyroid gland to become more active and release excess amounts of thyroid hormone into the blood. A TSI test measures the amount of thyroid stimulating immunoglobulin in your blood.
TSH receptor stimulating antibody; Thyroid stimulating immunoglobulin; Hypothyroidism - TSI; Hyperthyroidism - TSI; Goiter - TSI; Thyroiditis - TSI
How the Test is Performed
A blood sample is needed.
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. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
Why the Test is Performed
Your health care provider may recommend this test if you have signs or symptoms of an overactive thyroid (hyperthyroidism), including symptoms of:
- Graves disease
- Toxic multinodular goiter
- Thyroiditis (swelling of the thyroid gland caused by an overactive immune system)
The test is also done during the last 3 months of pregnancy to predict Graves disease in the baby.
The TSI test is most commonly done if you have signs or symptoms of hyperthyroidism but are unable to have a test called thyroid uptake and scan.
Normal values are less than 130% of basal activity.
Normal value ranges may vary slightly among different laboratories. Some laboratories use different measurements or may test different specimens. Talk to your provider about the meaning of your specific test results.
What Abnormal Results Mean
A higher-than-normal level may indicate:
- Graves disease (most common)
- Hashitoxicosis (very rare)
- Neonatal thyrotoxicosis
Veins and arteries vary in size from one person 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.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood buildup under the skin)
- Infection (a slight risk any time the skin is broken)
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Salvatore D, Davies TF, Schlumberger MJ, Hay ID, Larsen PR. Thyroid physiology and diagnostic evaluation of patients with thyroid disorders. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, eds. Williams Textbook of Endocrinology. 13th ed. Philadelphia, PA: Elsevier; 2016:chap 11.
Weiss RE, Refetoff S. Thyroid function testing. In: Jameson JL, De Groot LJ, de Kretser DM, et al, eds. Endocrinology: Adult and Pediatric. 7th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 78.
Reviewed By: Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.