Anthropometric Predictors of Hemoglobin A1c among Adults: NHANES 2003 to 2004 and 2013 to 2014, Nearly 10% of adult Americans have type 2 diabetes mellitus (DM), yet 25% are undiagnosed. Our purpose was to compare body mass index (BMI), waist circumference (WC), and waist-to-height ratio (WHtR) as predictors for type 2 DM in adults 40 to 59 yr of age. We hypothesized that BMI, WC, and WHtR would predict hemoglobin A1c (HbA1c) ≥6.5%, diagnostic of diabetes. Data from the National Health and Nutrition Examination Survey for 2003 to 2004 (N = 1069) and 2013 to 2014 (N = 906) were used in logistic regression models. There were differences in ethnic/racial distribution in the 2003 to 2004 and 2013 to 2014 sample. BMI, WC, and WHtR were higher in 2003 to 2004 than 2013 to 2014 (BMI, 29.5 vs 25.7 kg·m−2; WC, 99.8 vs 87.1 cm; WHtR, 0.59 vs 0.55, respectively, each P < 0.0001). In 2003 to 2004, WC (odds ratio = 2.65, 95% confidence interval = 1.57–4.48) and WHtR (odds ratio = 2.91, 95% confidence interval = 1.69–5.04) predicted HbA1c ≥ 6.5%, but BMI did not. In 2013 to 2014, BMI, WC, or WHtR did not predict HbA1c ≥ 6.5%. WC or WHtR may suggest risk of type 2 DM in some populations.