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OBJECTIVE -The purpose of this study was to examine the prevalence and correlates of elevated A1C in a large, nationally representative sample of adults without diabetes in the U.S.RESEARCH DESIGN AND METHODS -We analyzed data from 15,934 participants aged Ն20 years without diagnosed diabetes who had A1C measurements in the 1999 -2006 National Health and Nutrition Examination Survey, a crosssectional and nationally representative sample of the U.S. population.RESULTS -The overall prevalence of A1C Ͼ6% was 3.8%, corresponding to 7.1 million adults without diabetes in the U.S. population. Approximately 90% of these individuals had fasting glucose Ն100 mg/dl. Older age, male sex, non-Hispanic black race/ethnicity, hypercholesterolemia, higher BMI, and lower attained education were significantly associated with having a higher A1C level even among individuals with normal fasting glucose (Ͻ100 mg/dl) and after multivariable adjustment.CONCLUSIONS -A single elevated A1C level (A1C Ͼ6%) is common in the general population of adults without a history of diabetes and is highly reliable for the detection of elevated fasting glucose. Nondiabetic adults with elevated A1C are likely to have impaired fasting glucose and an array of other risk factors for type 2 diabetes and cardiovascular disease.

Background:  The aims of the present study were to demonstrate the reliability of HbA1c measurements during two time periods and to compare these measurements with HbA1c distribution in the general US population. Methods:  HbA1c was measured in 14 069 whole blood samples in the Atherosclerosis Risk in Communities (ARIC) study using different HPLC instruments across two time periods, namely 2003–2004 and 2007–2008. At the time of measurement, samples had been in storage at −70°C for up to 18 years. To assess differences in values, HbA1c measurements were repeated in 383 samples at both periods. Indirect comparisons were made by comparing our measurements against those from a nationally representative study. Results:  The coefficients of variation for quality control samples were 1.8% (n = 89) in 2003–2004 and 1.4% (n = 259) in 2007–2008. The correlation between measurements at the two time points was high (r = 0.99), but with a slight bias: 0.29% points higher in 2007–2008 vs 2003–2004 (n = 383; P < 0.0001). The comparison yielded the following Deming regression equation: y(2007–2008) = 0.073 + 1.034x(2003–2004). After alignment using this equation, the distribution of HbA1c in the ARIC study was similar to that in the national study using fresh samples. Conclusions:  Measurements of HbA1c from samples stored for up to 18 years are highly reliable when using state‐of‐the‐art HPLC instruments, but with some bias introduced over time. The HbA1c data now available in the ARIC study should be invaluable for investigations into the clinical utility of HbA1c as a diagnostic test for diabetes.

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