Racial and Ethnic Differences in Hemoglobin A1c among Patients with Impaired Glucose Tolerance in the Diabetes Prevention Program

Abstract

Objective To examine racial and ethnic differences in hemoglobin A1c (HbA1c) in people with Impaired Glucose Tolerance (IGT).

Research Design and Methods We studied 3,819 individuals ≥ 25 years of age with IGT found to be eligible to participant in the Diabetes Prevention Program. HbA1c 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, β-cell function, and insulin resistance.

Results Mean ± SD HbA1c was 5.91 ± 0.50%. Among Whites, HbA1c was 5.80 ± 0.44%, among Hispanics 5.89 ± 0.46%, among Asian American 5.96 ± 0.45%, among American Indians 5.96 ± 0.46% and among African Americans 6.19 ± 0.59%. Age, sex, SBP, DBP, BMI, fasting glucose, glucose area under the curve, corrected insulin response and insulin resistance were each independent predictors of HbA1c. Adjusting for these and other factors, mean HbA1c levels were 5.78% for Whites, 5.93% for Hispanics, 6.00% for Asian Americans, 6.12% for American Indians, and 6.18% for African Americans (p < 0.001).

Conclusions HbA1c 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, HbA1c may not be valid for assessing and comparing glycemic control across racial and ethnic groups or as an indicator of health care disparities.