Impact of A1C screening criterion on the diagnosis of pre-diabetes among U.S. adults.
OBJECTIVE
New clinical practice recommendations include A1C as an alternative to fasting glucose as a diagnostic test for identifying pre-diabetes. The impact of these new recommendations on the diagnosis of pre-diabetes is unknown.


METHODS
Data from the National Health and Nutrition Examination Survey 1999-2006 (n = 7,029) were analyzed to determine the percentage and number of U.S. adults without diabetes classified as having pre-diabetes by the elevated A1C (5.7-6.4%) and by the impaired fasting glucose (IFG) (fasting glucose 100-125 mg/dl) criterion separately. Test characteristics (sensitivity, specificity, and positive and negative predictive values) using IFG as the reference standard were calculated.


RESULTS
The prevalence of pre-diabetes among U.S. adults was 12.6% by the A1C criterion and 28.2% by the fasting glucose criterion. Only 7.7% of U.S. adults, reflecting 61 and 27% of those with pre-diabetes by A1C and fasting glucose, respectively, had pre-diabetes according to both definitions. A1C used alone would reclassify 37.6 million Americans with IFG to not having pre-diabetes and 8.9 million without IFG to having pre-diabetes (46.5 million reclassified). Using IFG as the reference standard, pre-diabetes by the A1C criterion has 27% sensitivity, 93% specificity, 61% positive predictive value, and 77% negative predictive value.


CONCLUSIONS
Using A1C as the pre-diabetes criterion would reclassify the pre-diabetes diagnosis of nearly 50 million Americans. It is imperative that clinicians and health systems understand the differences and similarities in using A1C or IFG in diagnosis of pre-diabetes.
Mann
Devin M
DM
Department of Medicine, Division of General Internal Medicine, Mount Sinai School of Medicine, New York, New York, USA. devin.mann@mssm.edu
Carson
April P
AP
Shimbo
Daichi
D
Fonseca
Vivian
V
Fox
Caroline S
CS
Muntner
Paul
P
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D005215:Fasting / Q000097:blood; D018149:Glucose Intolerance / Q000175:diagnosis / Q000453:epidemiology; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006801:Humans; D008875:Middle Aged; D011236:Prediabetic State / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology / Q000378:metabolism; D014481:United States; D055815:Young Adult
D001786:Blood Glucose; D006442:Glycated Hemoglobin