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.
Funding
The GRADE Study was supported by a grant from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) of the National Institutes of Health under Award Number U01DK098246. The planning of GRADE was supported by a U34 planning grant from the NIDDK (U34-DK-088043). The American Diabetes Association supported the initial planning meeting for the U34 proposal. The National Heart, Lung, and Blood Institute and the Centers for Disease Control and Prevention also provided funding support. The Department of Veterans Affairs provided resources and facilities. Additional support was provided by grant numbers P30 DK017047, P30 DK020541-44, P30 DK020572, P30 DK072476, P30 DK079626, P30 DK092926, U54 GM104940, UL1 TR000439, UL1 TR000445, UL1 TR001108, UL1 TR001409, 2UL1TR001425, UL1 TR001449, UL1 TR002243, UL1 TR002345, UL1 TR002378, UL1 TR002489, UL1 TR002529, UL1 TR002535, UL1 TR002537, and UL1 TR002548. Educational materials have been provided by the National Diabetes Education Program. Material support in the form of donated medications and supplies has been provided by Becton, Dickinson and Company, Bristol-Myers Squibb, Merck & Co., Inc., Novo Nordisk A/S, Roche Diagnostics, and Sanofi. The CGM devices were donated by Abbott Laboratories. The CGM Substudy received material support from Asahi Kasei Pharma Corporation through their US distributor, EKF Diagnostics and from Siemens Healthcare Diagnostics, Inc. Abbott Laboratories donated the Free Style LibreTM Pro for this sub-study but had no role in the sub-study's design, conduct, analysis or reporting. The manufacturers contributed the trial medications and supplies under clinical-trial agreements with the NIDDK but had no role in the design, conduct, or analysis of the trial. An independent data and safety monitoring board appointed by the NIDDK oversaw the conduct of the trial. The content of this manuscript is solely the responsibility of the authors and does not necessarily represent the official v
