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Objective: To determine whether the relationship between average glycemia (AG) levels and HbA1c differs across racial/ethnic groups.Research Design and Methods: A prospective sub-study of GRADE, a comparative effectiveness randomized trial conducted in 36 centers in the US. 1454 of the 5047 participants from the GRADE cohort, including 534 non-Hispanic White (NHW), 389 non-Hispanic Black (NHB), 327 Hispanic White (HW), and 204 of other racial/ethnic backgrounds, participated in the sub-study. Continuous glucose monitoring (CGM) performed for 10 days was used to calculate AG10. Immediately after CGM, HbA1c and glycated albumin were measured. Fasting glucose (FPG) and glucose area-under-the-curve (AUC) were derived from a 75-gram oral glucose tolerance test.Results: The relationship between AG10 and HbA1c was significantly different for NHB compared to NHW and the other racial/ethnic groups. HbA1c levels were 0.2 to 0.6 percentage points higher in NHB than in NHW for AG10 levels from 100 to 250 mg/dL. For an HbA1c of 7%, the AG10 was 11 mg/dL higher for NHW than for NHB. Similar findings were observed across races for the relationships of FPG and AUC with HbA1c and for the glucose measurements with glycated albumin levels. The differences in the relationship between AG10 and HbA1c across racial groups remained after adjustments for any demographic or other differences between the racial/ethnic subgroups. Conclusion: The relationship between several measures of glucose with HbA1c and glycated albumin consistently differed across races. These findings should be considered in setting treatment goals and diagnostic levels.
Nathan et al. (Mon,) studied this question.