Context: Subjects with normal glucose tolerance (NGT) but 1-h postload glucose ≥ 155 mg/dL (NGT-1h-high) exhibit an intermediate cardiometabolic risk profile between individuals with NGT and impaired glucose tolerance (IGT).
Objective: This study aimed to evaluate whether NGT-1h-high subjects have different cardiometabolic characteristics and an increased risk of type 2 diabetes compared with individuals with isolated impaired fasting glucose (IFG).
Setting, design, and patients: A cross-sectional analysis was performed on 595 nondiabetic subjects who underwent an oral glucose tolerance test and an euglycemic hyperinsulinemic clamp in an ambulatory care setting. In addition, a longitudinal analysis was performed on 392 individuals, who were reexamined after a followup of 5.2 ± 0.9 y.
Main outcome measures: Insulin sensitivity, beta-cell function, and risk of developing diabetes were measured.
Results: Subjects with NGT-1h-high have a significant reduction of peripheral insulin sensitivity and beta-cell function, assessed by the disposition index, compared with either 1-h postload glucose < 155 mg/dL (NGT-1h-low) or IFG individuals, but not compared with IGT. Among the 392 subjects studied in the longitudinal analysis the incidence rate of type 2 diabetes over the follow-up period was 2.9, 16.7, 12.5, and 31.4% for subjects with NGT-1h-low, NGT-1h-high, IFG, and IGT, respectively. In a Cox proportional hazard regression analysis the risk of developing diabetes for NGT-1h-high subjects was 4.02 (95% confidence interval [CI] 1.06-15.26); an even higher risk (6.67; 95% CI, 2.09-21.24) was observed in subjects with IGT, but not in the isolated IFG group (1.91; 95% CI, 0.44-8.29).
Conclusions: NGT-1h-high subjects exhibit a higher risk of developing diabetes than those with IFG or NGT-1h-low, likely due to decreased insulin sensitivity and beta-cell function.