DefinitionTSI stands for thyroid stimulating immunoglobulin. TSI stimulates the thyroid gland to enlarge and release excess amounts of thyroid hormone.This article discusses the test to determine the amount of TSI in your blood.Alternative NamesTSH receptor antibody; Thyroid stimulating immunoglobulinHow the test is performedBlood 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 you