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

Differences in A1C by Race and Ethnicity Among Patients With Impaired Glucose Tolerance in the Diabetes Prevention Program William H. Herman , MD, MPH 1 , Yong Ma , MS 2 , Gabriel Uwaifo , MD 3 , Steven Haffner , MD, MPH 4 , Steven E. Kahn , MB, CHB 5 , Edward S. Horton , MD 6 , John M. Lachin , SCD 2 , Maria G. Montez , RN, MSHP, CDE 7 , Tina Brenneman , BS 2 , Elizabeth Barrett-Connor , MD 8 and for the Diabetes Prevention Program Research Group * 1 Department of Internal Medicine and Epidemiology, University of Michigan Health System, Ann Arbor, Michigan 2 Biostatistics Center, George Washington University, Rockville, Maryland 3 Medstar Research Institute, Washington, DC 4 Department of Medicine, Clinical Epidemiology, University of Texas Health Science Center, San Antonio, Texas 5 Department of Medicine, VA Puget Sound Health Care System and University of Washington, Seattle, Washington 6 Section on Clinical Research, Joslin Diabetes Center, Boston, Massachusetts 7 Diabetes Prevention Program, University of Texas Health Science Center, San Antonio, Texas 8 Department of Family and Preventative Medicine, University of California at San Diego, La Jolla, California Address correspondence and reprint requests to William H. Herman, MD, Diabetes Prevention Program Coordinating Center, Biostatistics Center, George Washington University, 6110 Executive Blvd., Suite 750, Rockville, MD 20852. E-mail: dppmail{at}biostat.bsc.gwu.edu Abstract 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 ≥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), β-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. AUC, area under the curve CIR, corrected insulin response DPP, Diabetes Prevention Program FPG, fasting plasma glucose HOMA-IR, homeostasis model assessment of insulin resistance IGT, impaired glucose tolerance OGTT, oral glucose tolerance test Footnotes Published ahead of print at http://care.diabetesjournals.org on 29 May 2007. DOI: 10.2337/dc06-2003. * ↵ * A full list of the members of the Diabetes Prevention Program Research Group can be found in N Engl J Med 346:393–403, 2002. A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C Section 1734 solely to indicate this fact. Accepted May 21, 2007. Received September 25, 2006. DIABETES CARE