The prevalence of the 65-kilodalton isoform of glutamic acid decarboxylase autoantibodies by glucose tolerance status in elderly patients from the cardiovascular health study.

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: The objective of this study was 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 3318 participants from the Cardiovascular Health Study, a cohort study of 5888 individuals 65 or older.
Setting: The population-based cohort was recruited from four U.S. sites.
Patients: Patients included all Cardiovascular Health Study 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, body mass index, fasting glucose and insulin levels, blood pressure, lipid levels, and diabetes treatment at baseline were measured.
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, insulin only, and both oral hypoglycemic agents and insulin, respectively (P = 0.02, linear trend). Among diabetic participants, GAD65AA positivity was associated with diabetes treatment, higher fasting glucose, and lower body mass index.
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.