Used as an adjunct test in the prediction of type 1 diabetes and the differential diagnosis of type 1 versus type 2 diabetes. Prior to clinical onset, type 1 diabetes is often characterized by circulating autoantibodies against a variety of islet cell antigens, including glutamic acid decarboxylase (GAD),tyrosine phosphatase (IA), and insulin. The presence of these autoantibodies provides early evidence of autoimmune disease activity, and their measurement can be useful in assisting the physician with the prediction, diagnosis, and management of patients with diabetes.