OBJECTIVE To assess the performance of different cutoff points of fasting capillary glycemia (FCG) in the diagnosis of diabetes and impaired glucose tolerance (IGT) using the receiver operating characteristics (ROC) curve approach.

RESEARCH DESIGN AND METHODS This study included a sample of 4,019 subjects without a previous history of diabetes who were recruited for a confirmatory 2-h post-glucose challenge capillary glycemia from a larger sample of 21,847 individuals screened with FCG. The sensitivity and the specificity of FCG as a screening test were analyzed in the cutoff range 3.9–8.9 mmol/l, and the corresponding ROC curves were plotted to assess the performance of the test.

RESULTS The screening test performance was better for diabetes than for IGT in the full range of cutoff points studied. Sensitivities ranged between 37.9 and 97.1% for diabetes and 1.8 and 94.4% for IGT; the areas under the ROC curves were 0.91 ± 0.01 and 0.75 ± 0.01, respectively. The cutoffs showing the best equilibrium between sensitivity and specificity approached 5.6 and 5.0 mmol/l for diabetes and IGT, respectively. Factors such as age, color, and family history of diabetes can affect the screening test performance.

CONCLUSIONS ROC curves can provide useful information toward improving the usefulness of FCG as a screening test for abnormalities of glucose tolerance.