Abstract
INTRODUCTION: The post-biopsy International IgA Nephropathy Prediction Tool (IIgAN-PT) models were updated to assess progression risk 1 or 2 years after biopsy. This study externally validated both models in a contemporary Asian cohort with extended follow-up to evaluate long-term predictive performance. METHODS: We included 1,296 Chinese patients with biopsy-proven IgAN. The primary outcome was a composite of end-stage kidney disease or a 50% decline in estimated glomerular filtration rate (eGFR) within 1 year post-biopsy. Model performance was evaluated using the coefficient of determination (R (2)) and Akaike information criterion to assess model fit, concordance statistics (C-statistics) and Kaplan-Meier survival curves for discrimination, and the integrated calibration index (ICI) for calibration. Further analysis included net reclassification improvement (NRI), integrated discrimination improvement (IDI), and decision curve analysis. RESULTS: Over a median follow-up of 4.5 years (IQR: 2.2-7.6), 20.2% of patients experienced the primary outcome. Models with and without race demonstrated excellent performance, with R (2) of 81.0% and 80.2%. C-statistics for 4- and 5-year risk prediction were 0.89 and 0.87, respectively. Kaplan-Meier curves showed clear separation between risk strata, especially in the highest-risk group, who had lower baseline eGFR and a steeper decline. Calibration was good for both 4- and 5-year predictions as reflected by the ICI. Nonetheless, both models underestimated risk in the highest-risk group at these time points. Discrepancies became more apparent beyond 10 years, as confirmed by DCA. Compared to the original models, the updated models improved risk reclassification, as indicated by both NRI and IDI for 4- and 5-year risk prediction. CONCLUSION: The post-biopsy IIgAN-PT models demonstrated good predictive performance and may support individualized risk stratification and treatment decisions in IgAN.