The Width-Delay Index: a Glucose-Only OGTT Metric for Assessing Insulin Resistance

Background: Insulin resistance is a core pathophysiologic feature of metabolic disease, but its reference-standard assessment by steady-state plasma glucose (SSPG) testing is procedurally demanding and labor-intensive, limiting use in routine clinical care and large-scale research. Because OGTT glucose profiles are widely available, we aimed to develop a glucose-only metric to characterize dynamic glucose responses and estimate SSPG-measured insulin resistance. Methods: We developed the Width-Delay Index (WDI), a glucose-only OGTT metric integrating relative exposure width, delayed exposure timing, and glycemic floor. In a dataset of 32 subjects with 16-point venous OGTT profiles and paired SSPG measurements, WDI performance was assessed using leave-one-out cross-validation (LOOCV) for SSPG prediction, together with insulin-resistance discrimination and sparse-sampling robustness analyses. Results: The 15-120 min OGTT window yielded the strongest WDI performance. WDI15-120 predicted SSPG with LOOCV R2 = 0.57 (95% CI, 0.27-0.77), Pearson r = 0.77, and Spearman rho = 0.74. WDI15-120 showed higher predictive performance than standard OGTT glucose measures and insulin-derived indices, including HOMA-IR, Matsuda index, and disposition index. WDI15-120 also discriminated insulin-resistant from insulin-sensitive subjects with AUROC = 0.969. When recalculated from conventional 5-point OGTT sampling, WDI15-120 retained substantial performance, with LOOCV R2 = 0.41 and AUROC = 0.945. Conclusions: WDI provides a simple, glucose-only, physiologically interpretable approach for estimating SSPG-measured insulin resistance from OGTT glucose dynamics.