Comparison of fasting and 2-hour Glucose and HbA(1c) levels for diagnosing diabetes: Diagnostic criteria and performance revisited

OBJECTIVE: Nearly two decades ago, the National Diabetes Data Group (NDDG) and the World Health Organization (WHO) Expert Committee on Diabetes Mellitus published diagnostic criteria for diabetes. We undertook this study to compare the performance of three glycemic measures for diagnosing diabetes and to evaluate the performance of the WHO criteria. RESEARCH DESIGN AND METHODS - In a cross-sectional population-based sample of 1.018 Egyptians ≤ 20 years of age, fasting and 2-h glucose and HbA(1c) were 7.2 mmol/l (129 mg/dl), 11.5 mmol/l (207 mg/dl), and 6.7%, respectively. When diabetic retinopathy was used to define diabetes, ROC curve analyses found that fasting glucose of 7.8 mmol/l (140 mg/dl) was similar to a 2-h glucose of 12.2-12.8 mmol/l (220-230 mg/dl), and the performance of a 11.1 mmol/l (200 mg/dl) 2-h glucose was similar to a fasting glucose of 6.9-7.2 mmol/l (125- 130 mg/dl). CONCLUSIONS - Optimal cutpoints for defining diabetes differ according to how diabetes itself is defined. When diabetes is defined as the upper component of the bimodal population distribution, a fasting glucose level somewhat higher than the current WHO cutpoint minimized misclassification. When diabetic retinopathy defines diabetes, we found that the current fasting diagnostic criterion favors specificity and the current 2-h criterion favors sensitivity. These results should prove valuable for defining the optimal tests and cutpoint values for diagnosing diabetes.