Higher HbA1c Levels Should Be Used to Diagnose Diabetes and Prediabetes in Blacks

Blacks have higher HbA1c levels than whites with similar glucose levels, suggesting that universal diagnostic criteria could lead to overdiagnosis of diabetes and prediabetes in blacks. We hypothesized alternative HbA1c diagnostic criteria could reduce misclassification in blacks. Data from 3,603 non-Hispanic (NH) white (67.6%) and 1,721 NH black (32.4%), nonpregnant adults (18-70 year) were included from 5 cycles (2005-2014) of the National Health and Nutrition Examination Survey with HbA1c and plasma glucose measures (i.e., fasting and 2 hour from oral glucose tolerance test, OGTT). Diabetes and prediabetes by HbA1c was compared with ’true’ OGTT classification to identify alternative HbA1c values with the lowest misclassification (false positives + false negatives). Survey-weighted rates were computed across a series of HbA1c cutpoints for diabetes (HbA1c ≥5.7 to ≥7.3%) and HbA1c ranges for prediabetes (4.9-5.6% to 6.8-7.5%) in 0.1% increments. By ADA OGTT criteria, the prevalence of diabetes and prediabetes in whites was 4.6% and 42.1%, respectively, and in blacks, 4.2% and 36.9%. Under ADA criteria for diabetes, misclassification was similar in whites (3.7%) and blacks (3.5%), but blacks had 6.3 times the rate of false positives (1.1% blacks vs. 0.2%; p<0.001) and 0.76 times false negatives (57.3 vs. 75.1%, p=0.016). Diabetes misclassification was lowest in whites at HbA1c ≥6.3% (3.4% misclassified) and in blacks at ≥6.9% (3.2%). Prediabetes misclassification was similar in whites (35.8%) and blacks (33.9%), but blacks had 2.8 times the rate of false positives (24.5% vs. 8.6%; p<0.001) and 0.68 times that of whites (50.0 vs. 73.2%, p<0.001). Misclassification was lowest in whites at HbA1c 5.6-6.3% (34.3% misclassified) and in blacks at 5.9-6.6% (31.3%).

Conclusion: Overdiagnosis of diabetes and prediabetes is disproportionately high among NH blacks compared to NH whites. Increasing the HbA1c diagnostic thresholds by 0.3-0.6% for NH blacks could potentially avert 3.2 million false positives.