Use of HbA1c in Predicting Progression to Diabetes in French Men and Women

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Abstract
OBJECTIVE—Early identification of subjects at high risk for diabetes is essential, and random HbA1c (A1C) may be more practical than fasting plasma glucose (FPG). The predictive value of A1C, in comparison to FPG, is evaluated for 6-year incident diabetes. RESEARCH DESIGN AND METHODS—From the French cohort study Data from an Epidemiological Study on the Insulin Resistance Syndrome (DESIR), 1,383 men and 1,437 women, aged 30–65 years, were volunteers for a routine health check-up. Incident diabetes was defined by FPG ≥7.0 mmol/l or treatment by antidiabetic drugs. Multivariate logistic regression models were used to predict diabetes at 6 years. Receiver operating characteristic curves compared the predictive values of A1C and FPG. RESULTS—At 6 years, 30 women (2.1%) and 60 men (4.3%) had developed diabetes. Diabetes risk increased exponentially with A1C in both sexes (P < 0.001). After stratifying on FPG, A1C predicted diabetes only in subjects with impaired fasting glucose (IFG) (FPG ≥6.10 mmol/l): the odds ratio (95% CI) for a 1% increase in A1C was 7.20 (3.00–17.00). In these subjects, an A1C of 5.9% gave an optimal sensitivity of 64% and specificity of 77% to predict diabetes. CONCLUSIONS—A1C predicted diabetes, even though the diagnosis of diabetes was based on FPG, but it was less sensitive and specific than FPG. It could be used as a test if fasting blood sampling was not available or in association with FPG. In subjects with IFG, A1C is better than glucose to evaluate diabetes risk, and it could be used to select subjects for intensive early intervention.