Validation of the international IgA nephropathy prediction tool in a French cohort beyond 10 years after diagnosis

Abstract

Introduction The International IgA Nephropathy Network developed a tool (IINN-PT) for predicting the risk of End-Stage Renal Disease (ESRD) or a 50% decline in the estimated filtration rate (eGFR). We aimed to validate this tool in a French cohort with longer follow-up than previously published validation studies. Methods The predicted survival of patients with biopsy-proven IgAN from the Saint Etienne University Hospital cohort was computed with IINN-PT models with or without ethnicity. The primary outcome was the occurrence of either ESRD or a 50% decline in eGFR. The models’ performances were evaluated through c-statistics, discrimination, and calibration analysis. Results There were 473 patients with biopsy-proven IgAN, with a median follow-up of 12.4 years. Models with and without ethnicity showed AUCs [95%CI] of 0.817 [0.765;0.869] and 0.833 [0.791;0.875] and R2D of 0.28 and 0.29, respectively, and an excellent discrimination of groups of increasing predicted risk (p < 0.001). The calibration analysis was good for both models up to 15 years after diagnosis. The model without ethnicity exhibited a mathematical issue of survival function after 15 years. Discussion The IINN-PT provided good performances even after 10 years post-biopsy as showed by our study based on a cohort with a longer follow-up than previous cohorts (12.4 versus less than 6 years). The model without ethnicity exhibited better performances up to 15 years but became aberrant beyond this point due to a mathematical issue affecting the survival function. Our study sheds light on the usefulness of integrating ethnicity as a covariable for prediction of IgAN course.