On average, HbA1c levels may overestimate mean glucose concentrations in black people compared to white people, but race only partially explains the difference, according to a recent prospective observational study.
Researchers recruited 104 black people and 104 white people ages eight and older with type 1 diabetes from 10 diabetes centers in the U.S. Using continuous glucose monitoring (CGM) devices, they measured glucose concentrations for up to 12 weeks. They then calculated weighted mean glucose concentrations and compared by race with laboratory measurements of HbA1c, glycated albumin, and fructosamine levels. Results were published online on June 12 by Annals of Internal Medicine.
Overall, mean HbA1c level was 9.1% in black participants and 8.3% in white participants. When children were excluded, the mean HbA1c values were 8.6% and 7.9%, respectively. Using the CGM data, the study found that for a given HbA1c value, mean glucose concentration was significantly lower in black people than in white people (P=0.013). For a given mean glucose concentration, black people had mean HbA1c values that were 0.4 percentage points (95% CI, 0.2 to 0.6 percentage points) higher than those in white people. There were no significant differences between racial groups in the relationship of glycated albumin and fructosamine levels with mean glucose concentration.
The study authors concluded that mean HbA1c levels may overestimate mean glucose concentration in black people compared to white people, potentially because of differences in hemoglobin glycation. Irrespective of race, there may be individual variations in mean CGM glucose concentration for a given HbA1c level, they added.
Limitations of the study include the inclusion of only participants with type 1 diabetes and the use of CGM, which measures interstitial fluid rather than blood glucose, the authors acknowledged. “There is a possibility that differences between interstitial and blood glucose concentrations could have affected the results in unpredictable ways,” they wrote.
The authors of an accompanying editorial raised additional considerations, such as how CGM device readings were influenced by a single factory calibration in this study and are subject to interference from such common substances as vitamin C and aspirin. They added that a strength of the study was its inclusion (and finding of no significant difference) of glycated albumin and fructosamine, which “bolsters the evidence that the racial difference is a ‘hemoglobin-specific’ phenomenon.”
The editorialists emphasized that the study does not suggest that HbA1c has limited utility in black patients, adding that there is a need to better understand the subgroups that may be vulnerable to discordant HbA1c and glucose measures. “[S]uch groups may overlap with race, but we should not conflate such conditions with race itself,” they wrote.