HbA1c overestimates mean glucose in black persons compared with whites

1. Mean glucose concentration was significantly lower in black compared to white patients; however, HbA1c levels in black patients were higher than white patients.

2. Differences in glucose concentration with HbA1c may be attributed to racial differences in glycation of hemoglobin.

Evidence Rating Level: 2 (Good)

Study Rundown: Hemoglobin A1c (HbA1c) is used in standard clinical practice as a marker for glycemic control in diabetes patients. The results of this test are important, as they help guide diabetes management—particularly with respect to the use of drugs—as well as assess risk for diabetic complications. While higher HbA1c levels are usually observed in black patients, it is unclear as to whether this difference is due to differences in glycemic control or racial differences in the glycation of hemoglobin. Considering this debate, the authors of the study aimed to determine whether there is a racial difference in mean glucose and HbA1c for black patients compared to white patients. The main limitation of the study was that the results had to be interpreted in light of the inclusion criteria. Specifically, there were too few participants with HbA1c levels less than 6.5% to generalize the results to those individuals. Overall, the results of this study suggest that, on average, HbA1c levels overestimate mean glucose in black persons compared with whites. This difference may be due to racial differences in glycation of hemoglobin.

Click to read the study in the Annals of Internal Medicine

Relevant Reading: Racial and Ethnic Differences in the Relationship between HbA1c and Blood Glucose: Implications for the Diagnosis of Diabetes

In-Depth [prospective cohort]: In this prospective, 12-week observational study, 104 black patients and 104 white patients were included from 10 different diabetes centres in the United States. All study participants had type 1 diabetes with an HbA1c level of 6.0% to 12.0%. The study endpoints consisted of mean glucose concentration, glycated albumin, and fructosamine values. Generally, HbA1c levels were found to overestimate glucose concentration in black patients compared to white patients. Specifically, HbA1c values in black patients were 0.4 percentage points (95%CI 0.2 to 0.6 percentage point) higher than those in white persons for a given mean glucose concentration. In contrast, while glycated albumin and fructosamine values were highly correlated with HbA1c, no clinically significant racial differences were found in terms of their relationship with mean glucose concentration (p > 0.20 for each comparison).

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