Comparative performance of renal histological scores in predicting kidney outcomes in ANCA-associated vasculitis

BACKGROUND: Kidney involvement in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) remains a major determinant of adverse patient outcomes. Several histological and clinicopathological scoring systems have been proposed to predict kidney prognosis and guide treatment decisions. METHODS: This retrospective cohort study evaluated patients with kidney biopsy-proven AAV, diagnosed between January 2013 and December 2023. The primary endpoint was progression to end-stage kidney disease (ESKD). Cox regression analysis was used to evaluate clinical and histological predictors of ESKD. Kaplan-Meier analysis, Harrell's C-statistics, and Cramér's V were used to assess the performance and concordance of Berden classification, Mayo Clinic Chronicity Score (MCCS), Renal Risk Score (RRS), and Improved ANCA Kidney Risk Score (AKRiS). RESULTS: Of 53 included patients, 22.6% progressed to ESKD. Interstitial fibrosis and tubular atrophy ≥25% was the strongest histological predictor of ESKD, and MCCS (HR 1.574 95% CI 1.123-2.206), RRS (HR 1.405 95% CI 1.110-1.777) and AKRiS (HR 1.254 95% CI 1.090-1.442) proved to be independent predictors of ESKD. AKRiS showed the highest discriminative performance (C-statistic 0.871 95% CI 0.781-0.989) and differentiated kidney survival across all risk categories. Cross-comparison revealed significant concordance among low and high-risk groups of MCCS, RRS, and AKRiS. CONCLUSIONS: In a contemporary cohort of AAV, MCCS and AKRiS demonstrated the strongest predictive performance for ESKD. The combined use of histological and clinicopathological scores may improve risk stratification and support more personalized treatment decisions, particularly in patients with intermediate risk.