Aims: To examine the clinical utility of 30-min plasma glucose (30-min-PG) measurement during an oral glucose tolerance (OGTT) in predicting type 2 diabetes (T2DM).
Research design and methods: Data from a 3-year, randomized, controlled, primary prevention trial among 548 Asian Indians with prediabetes were analyzed. Participants underwent OGTT with PG measurements at fasting, 30-min, and 2-h at baseline and annually until the end of the study. Multivariable Cox regression models were constructed to calculate the risk of developing diabetes based on 30-min-PG levels. Improvement in prediction performance gained by adding an elevated level of 30-min-PG over prediabetic categories was calculated using the area-under-curve (AUC), net-reclassification (NRI), and integrated discrimination improvement (IDI) statistics.
Results: At the end of follow-up, 30.4% of individuals had been diagnosed with T2DM by ADA criteria. Based on the maximally selected log-rank statistics, the optimal 30-min-PG cut point for predicting incident T2DM was >182 mg/dl. Multivariable-adjusted Cox regression models showed an independent association between elevated 30-min-PG (>182 mg/dl) and incident diabetes (hazard ratio (95% CI): 1.85 [1.32, 2.59]; Dxy = 0.353, c-statistic = 0.676). The addition of an elevated 30-min-PG (>182 mg/dl) model significantly improved the prediction of diabetes (Δdeviance: -15.4; ΔAUC: 0.11; NRIcontinuous: 0.51; IDI: 0.08) compared with IFG model alone) in individuals with prediabetes.
Conclusion: In prediabetic individuals, baseline 30-min-PG independently predicted T2DM and significantly improved reclassification and discrimination. Therefore, 30-min-PG should be considered as part of the routine testing in addition to FPG and 2-h-PG for better risk stratification.
Keywords: 30-min-plasma glucose; Diabetes prediction; Net reclassification improvement; OGTT; Prediabetes; Predictive utility.
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