TSH receptor antibodies (TRAb) are autoantibodies that bind to the TSH receptor on thyroid cells, mimicking the action of TSH and causing the thyroid to produce excess hormone — the mechanism behind Graves' disease, the most common cause of hyperthyroidism. Unlike Anti-TPO and Anti-Tg, which are markers of inflammation, TRAb are directly causative of thyroid overactivity.

TRAb testing is used to confirm the diagnosis of Graves' disease, differentiate it from other causes of hyperthyroidism (such as toxic nodular goitre), predict the risk of relapse after antithyroid drug treatment, and monitor Graves' disease in pregnancy — where TRAb can cross the placenta and cause foetal or neonatal hyperthyroidism.