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 44623 participants aged 20 to 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=41411), 2-hour post oral glucose load plasma glucose (2-h PG; n=21334), and glycated hemoglobin (HbA1c; n=28010), was examined.

Results: When diabetes-specific retinopathy was plotted against continuous glycemic measures, a curvilinear relationship was observed for FPG and HbA1c. Diabetes-specific retinopathy prevalence was low for FPG < 6.0 mmol/L and HbA1c < 6.0% but increased above these levels. Based on vigintile (20 groups with equal numbers) distributions, glycemic thresholds for diabetes-specific retinopathy were observed over the range 6.4-6.8 mmol/L for FPG, 9.8-10.6 mmol/L for 2-h PG, and 6.3-6.7% for HbA1c. 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 HbA1c.

Conclusion: This study broadens the evidence-base on diabetes diagnostic criteria. A narrow threshold range for diabetes-specific retinopathy was identified for FPG and HbA1c 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 HbA1c of 6.5% is a suitable alternative diagnostic criterion.