Is the measurement of glycated hemoglobin A1c alone an efficient screening test for undiagnosed diabetes? Japan National Diabetes Survey.

The aim of the study was to assess the screening test properties of HbA1c for undiagnosed diabetes (DM) according to the 1999-WHO criteria and its relevance of the Japan National Diabetes Survey Cut-off points for possible and probable DM: HbA1c >or=5.6 and 6.1%. Screening properties of HbA1c predicting undiagnosed DM was examined and compared with that of fasting plasma glucose (FPG) in 1904 Funagata-town inhabitants aged 35-89 years old. The prevalence of previous DM, undiagnosed DM, and impaired glucose regulation (IGR) were 5.5, 6.0, and 18.6%, while the prevalence of probable and possible DM were 7.7 and 5.4%. The area under the receiver operating characteristic curve for undiagnosed DM was similar between HbA1c (0.856 [95% CI: 0.812-0.899]) and FPG (0.902 [0.869-0.936]). HbA1c of 5.6% gave a sensitivity of 56.5%, a specificity of 95.1%, positive and negative predictive values of 44.2 and 97.0%, and a proportion of people above the cut-off point of 8.2%. True positive tests were significantly higher with mean levels of BMI, fasting, and 2-h plasma glucose, and HbA1c, but lower with mean levels of high-density-lipoprotein cholesterol than in false negative tests. The measurement of HbA1c alone may be efficient to screen undiagnosed DM and the cut-off point of 5.6% might be proper with respect to screening tests properties for undiagnosed DM, and prediction of vascular complications in Japan.