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Many Diabetes Cases May Go Undetected By Afternoon Tests
Study suggests need for repeat testing for some patients

CHICAGO -- If current diagnostic criteria for diabetes are applied to patients tested in the afternoon, about half of cases of undiagnosed diabetes may be missed, according to an article in the December 27 issue of The Journal of the American Medical Association.

Rebecca J. Troisi, Sc.D., formerly of Social and Scientific Systems Inc., Bethesda, Md. (she is now with the National Cancer Institute), and Maureen I. Harris, Ph.D., M.P.H., and Catherine C. Cowie, Ph.D., from the National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Md., evaluated the variation in fasting plasma glucose levels in samples taken at different times of the day to examine whether diagnostic criteria based on morning measurements can be applied to patients who are tested for diabetes in the afternoon. They analyzed data from the U.S. population-based Third National Health and Nutrition Examination Survey (NHANES III), conducted between 1988 and 1994. Study participants aged 20 or older who had no previously diagnosed diabetes were randomly assigned to morning or afternoon examinations.

Current diagnostic criteria for diabetes are based on plasma glucose levels in blood samples obtained in the morning after an overnight fast, with a value of 7.0 mmol/L (126 mg/dL) or more indicating diabetes. But according to background information cited in the study, many patients are seen by their physicians in the afternoon in an uncertain state of fasting. Plasma glucose has also been observed to be higher in the morning.

For the current study, a total of 6,483 people tested in the morning were asked not to eat or drink anything other than water after 8:30 p.m. on the day preceding the examination. The median fasting time for those tested in the morning was 13.5 hours. The other 6,399 participants were tested in either early or late afternoon. Those tested in early afternoon were asked to eat breakfast but not to eat or drink anything other than water after 7:30 a.m. on the day of the test. Those examined in late afternoon were asked to eat lunch, but not to eat or drink anything other than water after 11:30 a.m. The median fasting time for those examined in the afternoon was 7.0 hours. Study participants in the morning and afternoon groups were similar in age, sex, race, parental history of diabetes, body mass index, waist-to-hip ratio, physical activity, smoking status, alcohol intake, education, use of medications that may affect glucose levels, and glycosylated hemoglobin levels.

"Fasting plasma glucose increased with age, but morning subjects had higher glucose values at every age compared with afternoon subjects, with an overall mean difference of 0.28 mmol/L (5.0 mg/dL)," the authors write.

"Consequently, prevalence in afternoon subjects of glucose values indicating diabetes (1.4 percent) was one half that of morning subjects (2.8 percent)," they continue, and suggest that the differences in fasting plasma glucose levels between subjects examined in the morning and afternoon were clinically significant.

"We estimate that glucose values indicating diabetes for patients tested in the afternoon should be fully 0.67 mmol/L (12 mg/dL) lower than the current diagnostic criterion of 7.0 mmol/L (126 mg/dL) or greater," they write. "If the current criterion were applied to afternoon patients, about half the cases of undiagnosed diabetes would be missed in this group."

"Regardless of the time of day that patients are tested, physicians need to confirm the diagnosis by repeat testing on a different day," the authors suggest. "For those initially tested in the afternoon, a confirmatory morning test may be advised."

(JAMA. 2000; 284:3157-3159)

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This release is reproduced verbatim and with permission from the American Medical Association as a service to reporters interested in health and behavioral change. For more information about JAMA or to obtain a copy of the study, please contact the American Medical Association's Science News Department at (312) 464-5374.