BACKGROUND: The issue of whether glucose concentrations below the diabetic threshold may be predictive of increased cardiovascular risk has not yet been fully elucidated. The current study evaluates the prognosis of nondiabetic patients with ischemic heart disease (IHD) and impaired fasting glucose (IFG) over a 7.7-year follow-up period. METHODS: A total of 11,853 patients with documented coronary artery disease aged between 45 and 74 years were examined. Patients were divided into 3 groups on the basis of their fasting blood glucose levels at screening: nondiabetic individuals, patients with IFG, and undiagnosed diabetic patients. Patients who were on any type of pharmacologic antidiabetic treatment were excluded from the study. Mortality rates were assessed separately for each group. RESULTS: The population comprised 9773 nondiabetic patients (82.4%, glucose up to 109 mg/dL), 1258 patients with IFG levels (10.6%, glucose 110-125 mg/dL), and 822 diabetic subjects (7%, glucose > or =126 mg/dL). Patients were followed up from 6.2 to 9.0 years (mean follow-up period 7.7 +/- 1.5 years). Crude mortality was lower in the nondiabetic subjects than in the 2 other groups. All-cause mortality in the nondiabetic group was 14.3% compared to 20.1% in patients with IFG and 24.3% in the undiagnosed (P <.001). Multivariate adjustment showed the lowest mortality in nondiabetic subjects, who exhibited a survival rate of 0.86 at the end of the follow-up, whereas the lowest survival-0.75-was seen among undiagnosed diabetic patients (P =.0001). An intermediate value of 0.78 was documented for patients with IFG (P <.01). After multivariate analysis, with nondiabetic patients as the reference group, IFG was identified as a consistent predictor of increased all-cause and IHD mortality with hazard ratios of 1.39 (95% confidence interval 1.21-1.59) and 1.29 (95% confidence interval 1.01-1.64), respectively. CONCLUSIONS: The main finding of this study is the substantially increased mortality rate among nondiabetic coronary patients with IFG, who had fasting glucose levels markedly lower than hitherto acknowledged as defining overt diabetes.