No ethnic differences in the association of glycated hemoglobin with retinopathy

OBJECTIVEdCurrent recommendations for the use of hemoglobin A1c (HbA1c) in diabetes screening and diagnosis aim to identify those at greatest risk for diabetic microvascular complications. However, there is current controversy regarding the clinical implications of ethnic differences in HbA1c values. The objective of this study was to determine whether the association between HbA1c and retinopathy differs by ethnic group in a representative sample of U.S. adults. RESEARCH DESIGN AND METHODSdThe study was a cross-sectional analysis of 2,945 non-Hispanic white, 1,046 non-Hispanic black, and 1,231 Hispanic American participants aged 40 years from the 2005-2008 National Health and Nutrition Examination Survey. RESULTSdAmong nondiabetic adults, the mean HbA1c was 5.5% in non-Hispanic whites, 5.7% in non-Hispanic blacks, and 5.6% in Hispanic Americans. Among those with diagnosed diabetes, mean HbA1c was 6.9% in non-Hispanic whites, 7.5% in non-Hispanic Blacks, and 7.7% in Hispanic Americans. Overall, non-Hispanic blacks had the highest prevalence of retinopathy. In multivariable logistic models, HbA1c clinical categories were strongly associated with prevalent retinopathy. However, the magnitude of the association did not differ by ethnic group (all P values for interaction 0.7). Similar results were observed with HbA1c modeled continuously (per one percentage point) and stratified by diabetes status (all P for interactions . 0.3). CONCLUSIONSdWe observed no ethnic differences in the association of HbA1c with retinopathy. These data do not support ethnic-specific cut points for HbA1c for diagnosis or screening of diabetes mellitus.