Background: Although glycated hemoglobin (HbA1c) is now recommended to diagnose diabetes, its test performance for diagnosis and prognosis is uncertain. Our objective was to assess the test performance of HbA1c against single and repeat glucose measurements for diagnosis of prevalent diabetes and for prediction of incident diabetes.
Design and Methods: Population-based analyses of 12,485 participants The Atherosclerosis Risk in Communities (ARIC) Study and a subpopulation of 691 participants in the Third National Health and Nutrition Examination Survey (NHANES III) with repeat test results.
Results: Against a single fasting glucose ≥126 mg/dl, the sensitivity (Sn) and specificity (Sp) of HbA1c ≥6.5% for detection of prevalent diabetes were 47% and 98%, respectively (AUC 0.892). Against repeated fasting glucose (3 years apart) ≥126 mg/dl, Sn improved to 67% and Sp remained high (97%) (AUC 0.936). Similar results were obtained in NHANES III against repeated fasting glucose 2 weeks apart. The accuracy of HbA1c was consistent across age, BMI, and race groups. For persons with fasting glucose ≥126 mg/dl and HbA1c ≥6.5% at baseline, the 10-year risk of diagnosed diabetes was 88% as compared to 55% among those persons with fasting glucose ≥126 mg/dl and HbA1c 5.7-<6.5%.
Conclusions: HbA1c performs well as a diagnostic tool when diabetes definitions that most closely resemble those used in clinical practice are used as the gold standard. The high risk of diabetes among initially undiagnosed persons with both elevated fasting glucose and HbA1c suggests a dual role for fasting glucose and HbA1c for prediction of diabetes.
- Received June 29, 2010.
- Accepted September 14, 2010.
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