Race Differences in Long-Term Diabetes Management in an HMO : Response to Adams et al. Free

Adams et al. (1) examined longitudinal differences in HbA_1c (A1C) between black and white diabetic members of an HMO. They found a small, but persistent, increase in A1C values in black subjects; however, there is an important omission in their study. There is no indication that the authors considered the potential effect of the presence of variant hemoglobins in the study subjects. Eight percent of black individuals are carriers of hemoglobin S (2) and are thus heterozygotes for an amino acid substitution in the hemoglobin β chain, which can alter A1C test results. The prevalence of this hemoglobinopathy in white Americans is much lower (3). A1C can give an inaccurate assessment of glycemia in patients with sickle hemoglobin. The magnitude of this perturbation is method dependent and is not linear over the entire glycohemoglobin range (4). The possible contribution of this effect to the observed differences in A1C described between black and white patients should have been considered. Failure to be aware of this can result in overtreating these patients, placing them at increased risk of hypoglycemia.

There are some test kits in commercial use that may eliminate interference by hemoglobin variants (5). The authors have not indicated, however, which assay method they used. Without this information and with no correlating blood glucose data, the presumption of racially based “psychosocial barriers to therapy intensification among patients and clinicians” (1) may be unwarranted.

Our efforts to achieve the best possible clinical outcome for our patients with diabetes by near normalization of blood glucose often focus on maintaining A1C levels as near normal as possible without undue hypoglycemia. While A1C is a valuable surrogate for glycemic control, current American Diabetes Association Clinical Practice Recommendations remind us that “[g]lycemic control is best judged by the combination of the results of the patient’s SMBG testing and the current A1C result” (6).