The optimal cutoff value of glycated hemoglobin for detection of diabetic retinopathy

With standardization of measurement of glycated hemoglobin (A1C), the International Expert Committee Report in 2009 and the American Diabetes Association in 2010 recommended incorporating A1C ≥6.5% into the previous diagnostic criteria using fasting plasma glucose and/or 2-hour plasma glucose. Whereas the association of A1C with cardiovascular diseases and other diabetic microvascular complications was linear without evidence of a distinct threshold, several studies suggested a threshold value for A1C in diabetic retinopathy (DR). In studies about the optimal cutoff value for A1C in DR, the A1C values range from 5.2% to 7.8%. There are several possible reasons why these values for DR differ so widely (differences in the definition and/or methods for DR, variation in statistical methods, differences in study population, differences in exclusion criteria, and difference in methods for measuring A1C). With these wide variations in the study method, drawing a conclusive cutoff value for A1C in DR is impossible. In published studies, the cutoff values for moderate or severe DR were higher than those for any or mild DR (6.4% to 7.0% vs. 5.5% to 6.5%).