Objective: An International Expert Committee (IEC) and the American Diabetes Association (ADA) proposed diagnostic criteria for diabetes and prediabetes based on A1c levels. We hypothesized that screening for diabetes and prediabetes with A1c measurements would differ from using oral glucose tolerance tests (OGTT).

Research Design and Methods: We compared prediabetes, dysglycemia (diabetes or prediabetes), and diabetes identified by proposed criteria (A1c≥6.5% for diabetes, and 6.0-6.4% [IEC] or 5.7-6.4% [ADA] for High Risk/prediabetes) to standard OGTT diagnoses in three datasets. NonHispanic white or black adults without known diabetes who had A1c and 75 g OGTT measurements were included from the prospective Screening for Impaired Glucose Tolerance study (SIGT, n=1581), and from NHANES III (n=2014), and NHANES 2005-2006 (n=1111).

Results: OGTT revealed prediabetes in 35.8% and diabetes in 5.2% of combined study subjects. A1c provided ROC areas for diabetes of 0.79-0.83, but ROC areas were ≤0.70 for dysglycemia or prediabetes. The proposed criteria missed 70% with diabetes, 71-84% with dysglycemia, and 82-94% with prediabetes. Compared to IEC, ADA criteria for prediabetes resulted in fewer false negatives and more false positives. There were also racial differences, with false positives more common in black subjects and false negatives more common in whites. Using NHANES 2005-2006 data, approximately 5.9 million nonHispanic U.S. adults with unrecognized diabetes and 43-52 million with prediabetes would be missed by screening with A1c.

Conclusions: The proposed A1c diagnostic criteria are insensitive and racially discrepant for screening, missing most undiagnosed Americans with diabetes and prediabetes.