Enhanced predictive capability of a 1-hour oral glucose tolerance test: A prospective population-based cohort study

OBJECTIVE To examine whether the 1-h blood glucose measurement would be a more suitable screening tool for assessing the risk of diabetes and its complications than the 2-h measurement. RESEARCH DESIGN AND METHODS We conducted a prospective population-based cohort study of 4,867men, randomly selected fromprespecified birth cohorts between 1921 and 1949,who underwent an oral glucose tolerance test with blood glucose measurements at 0, 1, and 2 h. Subjects were followed for up to 39 years, with registry-based recording of events. Discriminative abilities of elevated 1-h (≥8.6 mmol/L) versus 2-h (≥7.8 mmol/L) glucose for predicting incident type 2 diabetes, vascular complications, andmortality were compared using Kaplan-Meier analysis, Cox proportional hazards regression, and net reclassification improvement. RESULTS Median agewas 48 years (interquartile range [IQR] 48-49). During follow-up (median 33 years [IQR 24-37]), 636 (13%) developed type 2 diabetes. Elevated 1-h glucose was associatedwith incident diabetes (hazard ratio 3.40 [95% CI 2.90-3.98], P < 0.001) and provided better risk assessment than impaired glucose tolerance (Harrell concordance index 0.637 vs. 0.511, P < 0.001). Addition of a 1-hmeasurement in subjects stratified by fasting glucose provided greater net reclassification improvement than the addition of a 2-h measurement (0.214 vs. 0.016, respectively). Finally, the 1-h glucose was significantly associated with vascular complications and mortality. CONCLUSIONS The 1-h blood glucose level is a stronger predictor of future type 2 diabetes than the 2-h level and is associated with diabetes complications and mortality.