Progression to clinically diagnosed and treated diabetes from impaired glucose tolerance and impaired fasting glycaemia

Aims To evaluate the risk of diabetes in subjects with impaired fasting glycemia (IFG) as compared with impaired glucose tolerance (IGT) and normal glucose tolerance. Methods Men (1223) and women (1370) aged 45-64 years and free of diabetes at baseline were followed-up for 10 years, with 26 737 person years accumulated. The incident diabetic cases were identified through the national Drug Register and the Hospital Discharge Register. Results During the 10 years of follow-up, 53 (4.3%) men and 47 (3.4%) women developed diabetes. IFG alone defined 22 (15.5/1000 person years) diabetic cases, which was higher than for subjects with normal fasting glucose. Subjects with isolated IGT identified an additional 34 cases (155% more) which could not be defined by IFG alone. The area under the ROC curve was larger for 2-h glucose (0.77, 95% CI 0.72-0.82) than for fasting glucose (0.65, 0.58-0.71). The multivariate adjusted Cox hazard ratio was higher for isolated IGT (3.9, 95% CI 2.4-6.2) than for isolated IFG (2.3, 0.9-5.7) as compared with subjects with neither IFG nor IGT. Conclusion Both IFG and IGT are risk predictors for diabetes, but IGT defines a much larger target population for prevention.