Glycemic Thresholds for Diabetes-Specific Retinopathy Implications for diagnostic criteria for diabetes

OBJECTIVE — To re-evaluate the relationship between glycemia and diabetic retinopathy. RESEARCH DESIGN AND METHODS — We conducted a data-pooling analysis of nine studies from five countries with 44,623 participants aged 20–79 years with gradable retinal photographs. The relationship between diabetes-specific retinopathy (defined as moderate or more severe retinopathy) and three glycemic measures (fasting plasma glucose [FPG; n (cid:1) 41,411],2-hpostoralglucoseloadplasmaglucose[2-hPG; n (cid:1) 21,334],andA1C[ n (cid:1) 28,010]) was examined. RESULTS — When diabetes-specific retinopathy was plotted against continuous glycemic measures, a curvilinear relationship was observed for FPG and A1C. Diabetes-specific retinop- athy prevalence was low for FPG (cid:2) 6.0 mmol/l and A1C (cid:2) 6.0% but increased above these levels. Based on vigintile (20 groups with equal numbers) distributions, glycemic thresholds for dia- betes-specific retinopathy were observed over the range of 6.4–6.8 mmol/l for FPG, 9.8–10.6 mmol/l for 2-h PG, and 6.3–6.7% for A1C. Thresholds for diabetes-specific retinopathy from receiver-operating characteristic curve analyses were 6.6 mmol/l for FPG, 13.0 mmol/l for 2-h PG, and 6.4% for A1C. CONCLUSIONS — This study broadens the evidence based on diabetes diagnostic criteria. A narrow threshold range for diabetes-specific retinopathy was identified for FPG and A1C but not for 2-h PG. The combined analyses suggest that the current diabetes diagnostic level for FPG could be lowered to 6.5 mmol/l and that an A1C of 6.5% is a suitable alternative diagnostic criterion.