Comment on: Racial and individual variability in HbA1c–glucose relationship
In the thought-provoking study by Bergenstal et al, they explore a topic that is not widely appreciated: The imperfection of the HbA1c across racial groups. In this study the investigators compare A1c results versus continuous glucose monitoring (CGM)-obtained mean glucose readings in Black participants versus non-Hispanic White participants. They found that the HbA1c read 0.4% higher in Black participants despite similar levels of glucose by CGM. Further, they found that race did not affect the fructosamine or glycated albumin levels – other measures of glucose control. This study excluded people with hemoglobinopathies, anemia, pregnancy, renal disease, and recent transfusions—other commonly known entities that are known to alter the accuracy of HbA1c. The researchers reported that they did not have enough people with an A1c below 6.5% to provide a generalizable conclusion for those with prediabetes.
The authors summarize that HbA1c may actually overestimate glucose levels in Black patients with diabetes. While the exact mechanism was not identified it is believed that this is due to differences in glycation. This is quite important in that while there is international standardization of this value it is still not universal, and recognition of the need for collateral or alternative measures may be needed to assess mean glucose control in Black patients with diabetes. Clinicians should be reminded that while HbA1c is a valuable measure of glucose control over time, it has potential limitations in Black patients, and collateral glucose data including self-monitoring of blood glucose, continuous glucose monitoring, and other measures of intermediate control is needed to most accurately reflect true glucose control in Black patients with diabetes. Further research is needed to determine the true magnitude of this effect and if it is true across the spectrum of HbA1c.