The objective of this study was to compare the screening capacity of HbA1c versus fasting plasma glucose as a diagnostic test to identify individuals with pre-diabetes. Data from the National Health and Nutrition Examination Survey 1999-2006 (n=7,029) were analyzed. Results showed that the prevalence of pre-diabetes was 12.6% by the HbA1c criterion and 28.2% by the fasting glucose criterion. The use of HbA1c alone would reclassify 8.9 million people who would have been considered normal by fasting glucose as having pre-diabetes. On the other hand, the use of HbA1c alone will also reclassify 37.6 million people as not having pre-diabetes who would have been labeled as having pre-diabetes by the impaired fasting glucose criterion. These results suggest that the use of HbA1c as a recommended pre-diabetes diagnostic criterion will have a substantial impact on the number of U.S. adults identified as having pre-diabetes.