In Black Patients with Type 1 Diabetes, HbA1c Underestimates Mean Glucose

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Glycated hemoglobin (HbA1c) levels may underestimate mean glucose level in African Americans with type 1 diabetes, reports a study in Annals of Internal Medicine.

The T1D Exchange Racial Differences Study Group analyzed data on 104 non-Hispanic black and 104 non-Hispanic white patients with type 1 diabetes, enrolled at 10 US centers. (Individuals with anemia or hemoglobinopathy were excluded.) All subjects were at least 8 years old and had had type 1 diabetes for at least 2 years. Mean glucose concentration was measured by continuous glucose monitoring, and racial differences in the relationship between glucose and HbA1c were assessed.

In this population with type 1 diabetes, mean HbA1c was 9.1% in black subjects compared to 8.3% in white subjects; mean glucose concentration was 191 versus 180 mg/dL, respectively. At a given mean glucose concentration, HbA1c was 0.4 percentage point higher in blacks compared to whites. The results were similar on analysis of subjects with a higher number of continuous glucose monitoring measurements.

The racial difference in mean glucose–HbA1c relationship also persisted on stratified analysis by age under 18 years versus age 18 or older. Glycated albumin and fructosamine were highly correlated with HbA1c, with no clinically significant difference by race.

Studies have consistently reported higher HbA1c levels in black compared to white adults and children with type 1 or 2 diabetes. Although this could indicate poorer glycemic control in black patients, it might also reflect racial differences in glycation of hemoglobin.

This study suggests that HbA1c overestimates mean glucose concentration in black patients with type 1 diabetes. While this could reflect racial differences in hemoglobin glycation, race only partly explains the observed difference in HbA1c. The authors write, “Future research should focus on identifying and modifying barriers impeding improved glycemic control in black persons with diabetes” [Bergenstal RM, et al. Racial differences in the relationship of glucose concentrations and hemoglobin A1c levels. Ann Intern Med 2017; doi:10.7326/M16-2596].