Thyroid Stimulating Immunoglobulin (TSI) is a type of antibody that can be found in the blood of individuals with Graves’ disease, an autoimmune disorder that causes hyperthyroidism (overactive thyroid gland).
TSI antibodies bind to the same receptors in the thyroid gland that are normally stimulated by thyroid-stimulating hormone (TSH), leading to overproduction of thyroid hormones, including T3 and T4. TSI levels are often measured along with other thyroid function tests, such as TSH, Free T3, and Free T4, to help diagnose and monitor Graves’ disease.
TSI testing may also be used to distinguish between Graves’ disease and other causes of hyperthyroidism, such as a thyroid nodule or thyroiditis. TSI levels are typically not elevated in other causes of hyperthyroidism, making it a specific marker for Graves’ disease.
If you are experiencing symptoms of hyperthyroidism, such as weight loss, rapid heartbeat, anxiety, or tremors, or if you have a family history of Graves’ disease, your doctor may recommend a TSI test along with other thyroid function tests to help diagnose and monitor your condition.