Description
The Thyroid Stimulating Immunoglobulin (TSI) test measures a specific type of antibody that can cause the thyroid gland to become overactive, a condition known as Graves’ disease. TSI antibodies mimic the action of thyroid-stimulating hormone (TSH), leading to excess production of thyroid hormones (T3 and T4).
This test is particularly useful in diagnosing autoimmune thyroid conditions—especially Graves' disease, which is the most common cause of hyperthyroidism (overactive thyroid) in both men and women.
Purpose of the TSI Test
- Diagnose Graves' disease, even before symptoms are fully apparent
- Differentiate between types of hyperthyroidism (e.g., Graves' vs. thyroiditis or toxic nodules)
- Monitor disease progression or remission
- Evaluate risk of thyroid eye disease (Graves' orbitopathy)
What Are TSI Antibodies?
TSI antibodies are autoantibodies—they are produced by your immune system and target the TSH receptors on the thyroid gland, causing it to release more thyroid hormones than the body needs. This can result in a range of symptoms and complications if left untreated.
Symptoms of Graves' Disease / High TSI Levels
If you’re experiencing any of the following symptoms, this test may be appropriate:
- Unexplained weight loss
- Rapid or irregular heartbeat
- Anxiety or irritability
- Tremors (especially in the hands)
- Excessive sweating
- Bulging eyes (Graves’ orbitopathy)
- Heat intolerance
- Fatigue or muscle weakness
- Enlarged thyroid gland (goiter)
Test Details
- Sample Type: Blood draw
- Fasting Required: No
