Hemoglobin A_1c testing alone does not sufficiently identify patients with prediabetes

Whether hemoglobin A_1c (HbA_1c) values are suitable for diagnosing diabetes has been debated. We sought to assess the prevalence of elevated HbA_1c levels in a prediabetes patient population. Oral glucose tolerance tests and HbA_1c levels were analyzed for patients entering a diabetes prevention program between January 1, 2007, and September 13, 2009. We calculated the percentage of patients with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) who had HbA_1c values in the 6.0% to 6.4% range or in the 5.7% to 6.4% range. The mean age of the 242 patients was 62 years; 64.0% were women, and 88.0% were white. Isolated IFG was detected in about 56.2% of patients and combined IFG and IGT in about 37.2%. Only 28.5% of patients had HbA_1c values in the 6.0% to 6.4% range, whereas 65.3% had values in the 5.7% to 6.4% range. Our data suggest that reliance on HbA_1c testing alone to identify candidates for a diabetes prevention program would miss a substantial number of eligible patients.