Are There Clinical Implications of Racial Differences in HbA _1c? A Difference, to Be a Difference, Must Make a Difference

Abstract

Studies that have compared HbA _1c levels by race have consistently demonstrated higher HbA _1c levels in African Americans than in whites. These racial differences in HbA _1c have not been explained by measured differences in glycemia, sociodemographic factors, clinical factors, access to care, or quality of care. Recently, a number of nonglycemic factors and several genetic polymorphisms that operate through nonglycemic mechanisms have been associated with HbA _1c. Their distributions across racial groups and their impact on hemoglobin glycation need to be systematically explored. Thus, on the basis of evidence for racial differences in HbA _1c, current clinical guidelines from the American Diabetes Association state: “It is important to take…race/ethnicity…into consideration when using the A1C to diagnose diabetes.” However, it is not clear from the guidelines how this recommendation might be actualized. So, the critical question is not whether racial differences in HbA _1c exist between African Americans and whites; the important question is whether the observed differences in HbA _1c level are clinically meaningful. Therefore, given the current controversy, we provide a Point-Counterpoint debate on this issue. In the preceding point narrative, Dr. Herman provides his argument that the failure to acknowledge that HbA _1c might be a biased measure of average glycemia and an unwillingness to rigorously investigate this hypothesis will slow scientific progress and has the potential to do great harm. In the counterpoint narrative below, Dr. Selvin argues that there is no compelling evidence for racial differences in the validity of HbA _1c as a measure of hyperglycemia and that race is a poor surrogate for differences in underlying causes of disease risk.

—William T. Cefalu

Editor in Chief, Diabetes Care