Background/Purpose: Glomerulonephritis is a common and threatening manifestation in ANCA-associated vasculitis (AAV). To assess the risk of end-stage kidney disease (ESKD), various scores have been developed, with the ANCA renal risk score (ARRS) and the improved ANCA kidney risk score (AKRiS) [1] being introduced most recently. We aim to investigate its performance in granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) separately in comparison to histological finding.

Methods: We retrospectively analyzed 220 AAV cases between 1998 and 2021 who underwent renal biopsies and could be classified according to the 2020 ACR/EULAR criteria as either GPA or MPA. Follow-up visits were recorded every 6 months. The entire follow-up period was screened for the composite renal endpoint, which included death, dialysis, renal transplantation or the development or ESKD persistence with an eGFR < 15 ml/min/1.73 m² at or after six months of follow-up. The cases were analyzed according to histology and different risk scores. Comparison was done by Kaplan-Meier Curves, log-rank test and Herrell’s C.

Results: Histological analysis revealed that renal biopsies from MPA patients showed significantly more sclerosis, interstitial fibrosis and tubular atrophy. In terms of histological classification, most cases fell into focal and mixed classes, which mainly transitioned into low- and medium-risk AKRiS categories. Higher risk classifications predominantly derived from crescentic and sclerotic classes (Fig. 1). The substantial group categorized as medium risk most frequently transitioned to lower risk scores within AKRiS. Kaplan-Meier-plots document a clear stratification for the chosen renal end-point. The comparison of ARRS and AKRiS by ROC and the AUC analyzes revealed slightly higher values of the new AKRiS score with an AUC of 0.76 as opposed to ARRS with an AUC of 0.70 (Tabl. 1). The AUC was consistently slightly higher for MPA than for GPA in both risk scores and generally higher for AKRiS than for ARRS. AKRiS stratification proved effective for predicting the composite renal endpoint (area under the curve ≥0.7, C-Index 0.899). ARRS and AKRiS classified 67.7% of cases into the same risk category, while AKRiS assigned a lower risk category in 24.5% of cases and upgraded to a higher risk category in only 7.7% of cases.

Conclusion: The new AKRiS score was found to be effective not only in predicting ESKD but also in assessing a strong composite renal endpoint in a large European AAV cohort, despite slight differences in histological and event patterns between GPA and MPA under comparable treatment regimen.

Distribution of histological classification and their transformation into risk classes, color is taken from final AKRiS class to illustrate their origin and flow.

Histopathological findings and risk scores at diagnosis and outcomes of 220 patients having AAV with renal involvement.

Kaplan-Meier-plot of the composite renal endpoint for each risk group .

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/evolution-in-risk-stratification-for-renal-outcomes-in-anca-associated-vasculitides-using-established-scores-and-histopathological-criteria-in-a-large-european-cohort/