External validation of the international prediction tool in Korean patients with immunoglobulin A nephropathy

Abstract

Background: The International IgA Nephropathy Prediction Tool has been recently developed to estimate the progression risk of im-munoglobulin A nephropathy (IgAN). This study aimed to evaluate the clinical performance of this prediction tool in a large IgAN cohort in Korea.Methods: The study cohort was comprised of 2,064 patients with biopsy-proven IgAN from four medical centers between March 2012 and September 2021. We calculated the predicted risk for each patient. The primary outcome was occurrence of a 50% decline in estimated glomerular filtration rate (eGFR) from the time of biopsy or end-stage kidney disease. The model performance was evalu-ated for discrimination, calibration, and reclassification. We also constructed and tested an additional model with a new coefficient for the Korean race.Results: During a median follow-up period of 3.8 years (interquartile range, 1.8-6.6 years), 363 patients developed the primary out-come. The two prediction models exhibited good discrimination power, with a C-statistic of 0.81. The two models generally underesti-mated the risk of the primary outcome, with lesser underestimation for the model with race. The model with race showed better per-formance in reclassification compared to the model without race (net reclassification index, 0.13). The updated model with the Kore-an coefficient showed good agreement between predicted risk and observed outcome.Conclusion: In Korean IgAN patients, International IgA Nephropathy Prediction Tool had good discrimination power but underestimat-ed the risk of progression. The updated model with the Korean coefficient showed acceptable calibration and warrants external validation.