A1C to Detect Diabetes in Healthy Adults: When should we recheck?

OBJECTIVE: To evaluate the optimal interval for rechecking A1C levels below the diagnostic threshold of 6.5% for healthy adults. RESEARCH DESIGN AND METHODS: This was a retrospective cohort study. Participants were 16,313 apparently healthy Japanese adults not taking glucose-lowering medications at baseline. Annual A1C measures from 2005 to 2008 at the Center for Preventive Medicine, a community teaching hospital in Japan, estimated cumulative incidence of diabetes. RESULTS: Mean age (±SD) of participants was 49.7 ± 12.3 years, and 53% were male. Mean A1C at baseline was 5.4 ± 0.5%. At 3 years, for those with A1C at baseline of <5.0%, 5.0–5.4%, 5.5–5.9%, and 6.0–6.4%, cumulative incidence (95% CI) was 0.05% (0.001–0.3), 0.05% (0.01–0.11), 1.2% (0.9–1.6), and 20% (18–23), respectively. CONCLUSIONS: In those with an A1C <6.0%, rescreening at intervals shorter than 3 years identifies few individuals (∼≤1%) with an A1C ≥6.5%.