If your TSH test is abnormal (showing an overactive thyroid), this is the critical next step. The TSH Receptor Antibody test is the definitive, gold-standard blood test for diagnosing Graves' Disease, the most common cause of hyperthyroidism. This test detects the specific antibodies that are causing the problem by 'tricking' your thyroid into working overtime. This test doesn't just check function; it finds the autoimmune root cause, empowering your doctor with the precise diagnosis needed to build your treatment plan.