Prediction of Retinopathy at 20 Years After Onset in Younger-Onset Type 1 Diabetes Using Mean Metabolic Memory-Free HbA(1c) Values: The importance of using HbA(1c) data of total, not partial, diabetes duration

OBJECTIVE: Metabolic memory, in which past hyperglycemia could affect future retinopathy, is a potential issue in studying the relationship between glycemia and retinopathy. We examined retrospectively if mean “metabolic memory-free” glycosylated hemoglobin A1C (HbA(1c)) values covering total diabetes duration could predict retinopathy in younger-onset type 1 diabetes mellitus (T1DM). RESEARCH DESIGN AND METHODS: Inclusion criteria were T1DM onset before age 30 years, first visit to our center between 1988 and 1990 soon after onset, continuous HbA(1c) data for 20 years, and a 20-year follow-up retinopathy examination. Retinopathy predictive capabilities of HbA(1c) variables were examined. RESULTS: Of 15 subjects, 5 were retinopathy-positive and 10 were retinopathy-negative at the 20-year follow-up. Mean metabolic memory-free HbA(1c) values for the 20 years showed a substantial capacity to predict retinopathy at 20 years. The longer the period without HbA(1c) data following onset in simulation, the less accurate the prediction. CONCLUSIONS: HbA(1c) values may predict retinopathy better if metabolic memory-free data are used.