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 (approximately <or=1%) with an A1C >or=6.5%.