Thyroid Stimulating Immunoglobulin (TSI)

The TSI test measures the level of thyroid-stimulating immunoglobulin (TSI) in your blood. High levels of TSI in the blood can indicate the presence of Graves’ disease, which is an autoimmune disorder that affects the thyroid gland. If you have Graves’ disease, you’re more likely to develop other autoimmune diseases such as type 1 diabetes or Addison’s disease. Graves' disease is a classic form of hyperthyroid disease, affecting approximately 0.4% of the population of the United States. It is caused by IgG immunoglobulins, collectively known as thyroid stimulating immunoglobulins (TSI). Patients who are candidates for antithyroid drug therapy may not respond to this treatment when TSI levels are markedly elevated. The determination of TSI can also assist in predicting hyperthyroidism in neonates, due to placental transmission of the immunoglobulins from a mother with hyperthyroidism.