Islet Antigen-2 (IA-2) Autoantibody (IgG)

Islet Antigen-2 (IA-2) Autoantibody (IgG) is used to aid early recognition of autoimmune diabetes (type 1 diabetes mellitus) and to stratify risk in individuals at increased susceptibility. The assay helps differentiate type 1 diabetes from type 2 diabetes, distinguish LADA from type 2 diabetes, estimate the likelihood of progression in predisposed persons, and inform the probability that insulin therapy will be required in patients with diabetes. Synonyms used in clinical practice include anti-IA-2 antibody and ICA-512 autoantibody.

Type 1 diabetes mellitus arises from immune-mediated destruction of pancreatic beta cells, producing absolute insulin deficiency; overt hyperglycemia generally appears when more than 80% of beta cells have been lost. Autoantibodies to islet targets—such as GAD, IA-2, insulin, and ZnT8—often precede clinical onset by years and reflect active autoimmunity; the coexistence of multiple autoantibodies confers substantially greater future risk than a single specificity. IA-2 is a protein tyrosine phosphatase–like autoantigen localized to the dense-core granules of beta cells. IA-2 autoantibodies are present in approximately 50%–75% of patients at or before diagnosis, occur more frequently in children than in adults, and correlate with more aggressive beta-cell destruction. Antibody concentrations may decline over time as antigen availability wanes, reducing diagnostic yield in long-standing disease. Reported performance characteristics include sensitivity of about 57% and specificity of about 99% for type 1 diabetes; in children with elevated IA-2 autoantibodies, 5‑year risk of insulin-dependent diabetes has been estimated at approximately 65%. IA-2 autoantibodies are detected less often in LADA than in childhood-onset disease.