Thyrotropin receptor antibody (TRAb), also known as thyroid-stimulating antibody (TSAb) or thyroid-stimulating immunoglobulin (TSI), is an autoantibody to the thyroid gland that is produced during the autoimmune process of toxic diffuse goiter and stimulates the production of thyroid hormones by the thyroid gland. This antibody can be measured in the serum of approximately 80% to 100% of patients with toxic diffuse goiter, whereas it is rarely measured in patients with other types of hyperthyroidism. Therefore, the measurement of TRAb is of great value in identifying the various types of hyperthyroidism and is also used to evaluate the efficacy in the treatment of hyperthyroidism.