Differences in A1C by Race and Ethnicity Among Patients With Impaired Glucose Tolerance in the Diabetes Prevention Program

OBJECTIVE: We sought to examine racial and ethnic differences in A1C in individuals with impaired glucose tolerance (IGT). RESEARCH DESIGN AND METHODS: We studied 3,819 individuals aged > or = 25 years with IGT who were found to be eligible to participant in the Diabetes Prevention Program. A1C was compared among five racial and ethnic groups before and after adjustment for factors that differed among groups or might affect glycemia including age, sex, education, marital status, blood pressure, adiposity (BMI and waist circumference), hematocrit, fasting and post-glucose load glucose levels, glucose area under the curve (AUC), beta-cell function, and insulin resistance. RESULTS: Mean +/- SD A1C was 5.91 +/- 0.50%. Among whites, A1C was 5.80 +/- 0.44%, among Hispanics 5.89 +/- 0.46%, among Asian 5.96 +/- 0.45%, among American Indians 5.96 +/- 0.46%, and among blacks 6.19 +/- 0.59%. Age, sex, systolic blood pressure, diastolic blood pressure, BMI, fasting glucose, glucose AUC, corrected insulin response, and insulin resistance were each independent predictors of A1C. Adjusting for these and other factors, mean A1C levels were 5.78% for whites, 5.93% for Hispanics, 6.00% for Asians, 6.12% for American Indians, and 6.18% for blacks (P < 0.001). CONCLUSIONS: A1C levels are higher among U.S. racial and ethnic minority groups with IGT after adjustment for factors likely to affect glycemia. Among patients with IGT, A1C may not be valid for assessing and comparing glycemic control across racial and ethnic groups or as an indicator of health care disparities.