Does Race Alter the Relationship Between HbA1c and Glucose in Type 2 Diabetes?

Objective: Hemoglobin A1c (HbA1c) is the standard measurement of glycemic control, and the HbA1c value can be used to estimate average glucose using a formula. Several studies suggest that the relationship between average glucose and HbA1c may be different for Blacks. This project enrolled non-Hispanic black and white individuals with type 2 diabetes and evaluated the relationship between HbA1c and blood glucose. Method: 22 black and 29 white adults with type 2 diabetes were included in the analysis. Approximately 42 measurements (fasting and postprandial glucose) were collected over three months and compared to HbA1c of the third month. The effect of race was evaluated by ANCOVA and χ² analysis testing the slope and intercepts simultaneously for HbA1c and its relationship to fasting glucose and to postprandial glucose. Results: The relationship between HbA1c and glucose was not statistically significantly different between Blacks and Whites (ANCOVA: P = 0.968 for fasting glucose, P = 0.428 for postprandial glucose), allowing us to calculate estimated fasting and postprandial glucose disregarding race. For fasting glucose, the linear regression is FGmg/dl = (18.939 X HbA1c%) – 1.864, R² = 0.586, P < 0.0001. For postprandial glucose, the linear regression is ln(PPGmg/dl) = (1.261 X ln(HbA1c%)) + 2.555, R² = 0.614, P < 0.0001. Predicted values for postprandial glucose based on HbA1c were similar to estimated average glucose values reported by ADAG. Conclusion: This study reinforces the A1c-Derived Average Glucose (ADAG) group finding that the relationship between HbA1c and glucose is similar in non-Hispanic black and white adults with type 2 diabetes. ABBREVIATIONS:FG: fasting glucose; PPG: postprandial glucose; HbA1c: Hemoglobin A1c; eAG: estimated average glucose; ADAG: A1c Derived Average Glucose Study; UKPDS: United Kingdom Prospective Diabetes Study; NHANES: National Health and Nutrition Examination Survey; SIGT: Screening for Impaired Glucose Tolerance Study; DCCT: Diabetes Control and Complications Trial; AUC: area under the curve; HPLC: high performance liquid chromatography