SAN DIEGO – Having a hemoglobin A1c level of 5.7%-6.4% or impaired fasting glucose each predicted a sixfold higher risk for developing diabetes among individuals screened for the disease, and people who meet both criteria are at a 32-fold increased risk for diabetes, compared with normoglycemic individuals, a large longitudinal study found.
Using the two tests together could better identify people who are most likely to progress to diabetes and who could therefore benefit from early interventions, Yoriko Heianza and her associates reported at the annual scientific sessions of the American Diabetes Association. The findings simultaneously were published online (Lancet 2011 [doi:10.1016/S0140-6736(11)60472-8]).
The study followed 6,241 Japanese subjects, most of whom were government employees and who did not have diabetes at the time of their annual health screenings between 1997 and 2003, and who had annual exams for the next 4-5 years. During that time, 5% developed diabetes, an incidence similar to that in the general Japanese population.
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Ms Yoriko Heianza
At the baseline exam, 2,092 (34%) were diagnosed with prediabetes. Of those, nearly 20% were diagnosed with prediabetes solely on the basis of an HBA1c level of 5.7%-6.4% and 61% were diagnosed solely based on impaired fasting glucose, defined as a fasting plasma glucose concentration of 5.6-6.9 mmol/L. The remaining nearly 20% met both criteria for prediabetes, reported Ms. Heianza of the University of Tsukuba (Japan) Institute of Clinical Medicine and Toranomon Hospital, Tokyo.
Only half of the people who were diagnosed with prediabetes based on HbA1c level also had impaired fasting glucose, and only 24% of people diagnosed by impaired fasting glucose also met the HbA1c criterion.
Although the HbA1c test identified fewer individuals with prediabetes (822) than did impaired fasting glucose (1,680), the predictive power for progression to diabetes was similar between tests. Once diagnosed with prediabetes with either test, the risk for developing diabetes was six-fold higher than in normoglycemic individuals, after adjusting for the effects of age, sex, and other factors.
Meeting both criteria significantly increased the risk of developing diabetes to a level 32 times higher than in normoglycemic participants. The predictive power of using both tests is multiplied rather than simply additive, the investigators suggested.
The discordance between prediabetes diagnoses made by either HbA1c level or impaired fasting glucose in this study was similar to results from the U.S. National Health and Nutrition Examination Survey (NHANES), they added. In the current study, 19.7% met the HbA1c criterion for prediabetes without having impaired fasting glucose, compared with 17% in the NHANES data. In NHANES, the HbA1c test had a 27% sensitivity and a 93% specificity for diagnosing prediabetes, compared with a sensitivity of 21% and a specificity of 91% in the Japanese cohort.
Subjects in the Japanese study ranged in age from 24-82 years, with a mean age of 50 years; 75% were men.
Differences in baseline characteristics made up different cardiovascular risk profiles between individuals diagnosed with prediabetes solely based on HbA1c level or impaired fasting glucose. People diagnosed with prediabetes solely on the HbA1c criterion were more likely to be female and older, and less likely to be hypertensive or obese. They also had lower levels of triglyceride, uric acid, and HDL cholesterol.
The investigators reported having no conflicts of interest. The study was funded in part by Japan’s Ministry of Health, Labor and Welfare.