The prevalence of elevated hemoglobin A1c levels in adults without a history of diabetes is 3.8%, based on an analysis of data from the National Health and Nutrition Examination Survey.
This indication of a significant prevalence of undiagnosed diabetes was seen in an evaluation of data from 15,934 men and women aged 20 years and older. All had HbA1c measured during their participation in NHANES 1999–2006. Elevated HbA1c was defined as a level higher than 6%, and normal fasting glucose was defined as a level below 100 mg/dL.
The 3.8% overall prevalence of elevated HbA1c levels seen in this population translates into 7.1 million American adults. About 90% of the individuals with high HbA1c values also had fasting glucose levels that were 100 mg/dL or higher.
Elevated HbA1c values were significantly associated with male sex, advanced age, nonwhite race/ethnicity, hypercholesterolemia, a high body mass index, and a low level of education. The associations remained even for study participants with elevated HbA1c levels and normal fasting glucose values, according to Elizabeth Selvin, Ph.D., of the department of epidemiology at the Johns Hopkins University, Baltimore, and her associates.
Non-Hispanic blacks had higher rates of elevated HbA1c values, compared with other ethnic groups; however, the explanation for this association remains unclear. “Further research should be conducted to determine whether this disparity stems from racial differences in postprandial glycemia or from racial differences in the tendency of hemoglobin to undergo glycosylation,” the researchers stated (Diabetes Care 2009;32:828–33).
Dr. Selvin and her associates acknowledged the study's limitations, including its cross-sectional design and the fact that only one measurement of fasting glucose was taken. (The American Diabetes Association recommends repeating an elevated fasting glucose result.)
HbA1c values have been proposed for the screening and diagnosis of diabetes. The advantages of using HbA1c rather than glucose measures include the test's widespread availability and the fact that patients do not need to fast, as well as the “high repeatability of the measurement and the high specificity of elevated values,” the researchers wrote.
Although it “seems reasonable to adopt a single elevated A1c value as being diagnostic for diabetes … the real test of utility for A1c as a screening or diagnostic test of diabetes is its association with long-term clinical outcomes in an initially nondiabetic population specifically in comparison with fasting glucose levels,” they said.
The study was supported by grants from the National Institutes of Health/National Institute of Diabetes and Digestive and Kidney Diseases.
The authors disclosed no conflicts.