Applicability of a combination of hemoglobin A1c and fasting plasma glucose in population-based prediabetes screening

Background: The purpose of this study is to determine: (i) the concordance between a combination of hemoglobin A1c (HbA1c) and fasting plasma glucose (FPG) (HbA1c + FPG) and a combination of FPG and 2-h plasma glucose (2hPG) (FPG + 2hPG); and (ii) whether substituting FPG + 2hPG with HbA1c + FPG can enhance the detection of prediabetes in diabetes-free non-Hispanic Whites, non-Hispanic Blacks, and MexicanAmericans adults. Methods: Data (n = 1376) from the 2007 to 2008 U.S. National Health and Nutrition Examination Surveys were used for this investigation. Prediabetes cut points were determined using 5.76.4%, 100125, and 140199 mg/dL for HbA1c, FPG, and 2hPG, respectively. Concordances between HbA1c and FPG, HbA1c and 2hPG, HbA1c + FPG and FPG + 2hPG in screening for undiagnosed prediabetes were determined using sensitivity, specificity, and positive and negative likelihood ratios. Results: The overall concordance between HbA1c + FPG and FPG + 2hPG in screening for prediabetes was high, as indicated by a sensitivity of 92.4% (95% CI = 90.594.5) and specificity of 84.1% (81.287.0). The application of HbA1c + FPG was associated with a higher prevalence of prediabetes compared to FPG + 2hPG. Compared with FPG + 2hPG, screening with HbA1c + FPG was associated with 3.2%, 24.3%, and 4.2% relative increases in the identification of prediabetes in nondiabetic non-Hispanic Whites, non-Hispanic Blacks and MexicanAmericans, respectively. Conclusions: The enhanced prevalence of prediabetes using HbA1c + FPG compared with FPG + 2hPG calls for the need to redefine at a more basic and practical level how to apply HbA1c in screening for prediabetes. A redefined HbA1c that incorporates FPG, age, race/ethnicity, and body mass index may be a better way to use HbA1c in population-based and clinical settings.