A1C and Diabetes Diagnosis: The Rancho Bernardo Study

OBJECTIVE: To examine the sensitivity and specificity of A1C as a diagnostic test for type 2 diabetes in older adults. RESEARCH DESIGN AND METHODS: Cross-sectional study of community-dwelling adults without known diabetes who had an oral glucose tolerance test and A1C measured on the same day. RESULTS: Mean age of the 2,107 participants was 69.4 ± 11.1 years; 43% were men. Based on the American Diabetes Association (ADA) criteria, 198 had previously undiagnosed type 2 diabetes. The sensitivity/specificity of A1C cut point of 6.5% was 44/79%. Results were similar in age- and sex-stratified analyses. Given the A1C cut point of 6.5%, 85% of participants were classified as nondiabetic by ADA criteria. CONCLUSIONS: The limited sensitivity of the A1C test may result in delayed diagnosis of type 2 diabetes, while the strict use of ADA criteria may fail to identify a high proportion of individuals with diabetes by A1C ≥6.5% or retinopathy.