HbA1c may overestimate mean glucose for some Black patients with diabetes
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Key takeaways:
- Black patients with diabetes have a higher HbA1c than white patients with the same mean glucose.
- Two-thirds of the variance between mean glucose and HbA1c was found within racial-ethnic groups.
HbA1c may overestimate blood glucose values among Black patients with diabetes, according to study results published in Diabetes Technology & Therapeutics.
In a retrospective study of patients with type 1 or type 2 diabetes, Black patients who had the same mean glucose value measured through continuous glucose monitoring as white patients with diabetes had a 0.28 percentage points higher HbA1c. Differences were not observed between other racial-ethnic groups.
“Previous studies have found that HbA1c may not accurately reflect average blood glucose in some Black patients,” Andrew J. Karter, PhD, senior research scientist at Kaiser Permanente Division of Research, told Healio. “Our study confirms this on a population level and quantifies that, on average, HbA1c results for Black patients are about 0.3 percentage points higher than white patients with similar average blood glucose; results among Asians, Latinos and multiethnic patients did not differ from white patients. The findings are important because elevated HbA1c results could lead to premature diabetes diagnoses, overtreatment or invalid assessments of health disparities if based solely on HbA1c.”
Karter and colleagues conducted a retrospective study of data from 1,788 people with diabetes who attended Kaiser Permanente Northern California health system, had at least one HbA1c measurement available from 2016 to 2021 and had CGM data available for 90 days prior to an HbA1c measurement. HbA1c values were collected during routine visits and mean glucose was calculated using CGM data.
The study group included 1,295 non-Hispanic white patients, 187 Latino patients, 141 Asian patients, 94 Black patients and 71 multiethnic patients. Of the participants, 79% had type 1 diabetes. The mean HbA1c across all measurements was 7.4% and the mean glucose was 171 mg/dL.
In a fully adjusted model, Black patients with diabetes who had the same mean glucose as white participants had a 0.28 percentage points higher mean HbA1c (P < .0001). After stratifying by diabetes type, Black participants with type 1 diabetes had a 0.26 percentage point higher HbA1c and those with type 2 diabetes had a 0.31 percentage point higher HbA1c than white patients with the same mean glucose. Asian, Latino and multiethnic participants did not have any differences in HbA1c compared with white participants with the same mean glucose.
The researchers found that 65% of the variance between mean glucose and HbA1c was within racial-ethnic groups, 27% was within individuals and 9% was between racial-ethnic groups.
“Treatment decisions driven by guideline-based HbA1c targets should be individualized and supported by direct measurement of blood glucose,” Karter said. “Most clinicians who treat people with diabetes are aware that in some patients HbA1c is a poor indicator of average blood glucose. That said, while it is more likely that HbA1c overestimates blood glucose in Black patients, clinicians should not assume that this is true for all Black patients or that this is not happening in patients of other races or ethnicities.”
Karter said best practice for identifying people who may have variation between HbA1c and mean glucose needs to be explored. On a population level, Karter said more health policy research is needed to determine whether and how to account for possible overestimates of HbA1c.
For more information:
Andrew J. Karter, PhD, can be reached at andy.j.karter@kp.org.
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