Context: Autoantibodies (AA) to glutamic acid decarboxylase (GAD65), a determinant of risk for autoimmune diabetes, have been found in up to 10% of patients with Type 2 diabetes. In older adults this marker may also serve as a determinant of risk for autoimmune diabetes and enhance diabetes classification.

Objective: To evaluate the relationship between GAD65AA and glucose tolerance status, current diabetes treatment, and clinical measures in older adults.

Design: GAD65AA were measured at baseline in 3,318 participants from the Cardiovascular Health Study (CHS), a cohort study of 5,888 individuals 65.

Setting: Population-based cohort recruited from 4 U.S. sites.

Patients: All CHS participants with known diabetes, newly diagnosed diabetes, impaired fasting glucose, impaired glucose tolerance, and a sample of normal glucose tolerant participants.

Main Outcome Measures: GAD65AA, BMI, fasting glucose and insulin levels, blood pressure, lipid levels, and diabetes treatment at baseline.

Results: The prevalence of GAD65AA increased with decreasing glucose tolerance in both Blacks (n = 560) and Whites (n = 2730), being more pronounced in known diabetic individuals. GAD65AA were found in 2.3%, 5.8%, 7.8%, and 8.3% of diabetic participants, reporting use of no diabetes medication, oral hypoglycemic agents (OHGA), insulin only, and both OHGA and insulin, respectively (P = 0.02, linear trend). Among diabetic participants, GAD65AA positivity was associated with diabetes treatment, higher fasting glucose, and lower BMI.

Conclusions: Even among older individuals with diabetes, GAD65AA may be a useful marker in identifying a subgroup of autoimmune diabetes, serve as a marker of insulin requirement, and remain stable over years.