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Background: Recently, many studies were performed to evaluate the diagnostic value of fasting plasma glucose to diagnose diabetes, and the diagnostic criteria were revised by ADA in 1997 to avoid discrepancy between the fasting plasma glucose (FPG) and 2 hour post-load plasma glucose(2hPG) cutpoint values after 75g oral glucose loading and to alsc facilitate and encourage the use of test for diagnosing diabetes. This study was performed to assess the performance of different cutpoint of fasting plasma glucose in the diagnosis of diabetes and to compare the prevalence and incidence of diabetes using revised 1997 ADA FPG criterion with those using 1985 WHO criteria in Yonchon County of Korea. Methods: Two thousand three hundred fifty-six subjects who participated in population based cross- sectional study in Yonchon County in 1993. We have also analysed the data from 1141 subjects who were non-diabetic in 1993 and participated in the follow-up survey in 1995. The relationship between FPG and 2hPG were determined using sensitivity, specificity and the prevalence of diabetes according to FPG and/or 2hPG values. We have determined the prevalence and the incidence of diabetes using the ADA criterion. Results: Based on WHO criteria, a FPG of 6.1 mmol/L(110mg/dL) was determined to yield optimal sensitivity(83.6%) and specificity(82.4%), but it showed low positive predictive value(27.2%) and high prevalence(24.5%). The FPG cutpoint which showed same prevalence with the criterion ot the 2hPG >11.1mmol/L(87 in 2251) was 7.4mmol/L (133mg/dL, 87 in 2251), The crude prevalence of diabetes and impaired fasting glucose by ADA criterion were 9.6% and 14.9%, respectively, where as the crude prevalence of diabetes and IGT were 9.4% and 11.5% by WHO criteria. The crude incidence of diabetes was 5.1% as defined by ADA criterion and 34.4% of subjects who showed impaired fasting glucose in 1993 converted to diabetes in 1995, whereas the incidence was 2.5% by WHO criteria and 13% of IGT subjeets converted to diabetes in 2 years. Conclusions: The adequate cutpoint for FPG seems to lie between 6.1mmol/L and 7.4mmol/L. The 1997 ADA criterion of the FPG > 7.0mmol/L produced similar prevalence and higher incidence than those obtained from 1985 WHO criteria and the former seems to be better to detect the risk group who may progress to diabetes.