ANCA Kidney Risk Score Performance in a German Cohort of Patients with Histologically Confirmed ANCA-Associated Renal Vasculitis

Background Predicting the outcome of ANCA-associated vasculitis is a difficult task. One of the most promising prognostic scores, the ANCA renal risk score, has recently been updated and renamed to ANCA kidney risk score (AKRiS). We wanted to test its performance in our population. Methods In total, 164 patients were included and categorized in subgroups analogous to that of both scores. Multivariable logistic regression analysis was applied to assess the risk of renal failure. In addition, baseline data and outcome were compared between the subgroups of each score to retrieve useful clinical information. Results Stratified by AKRiS category, the proportions of patients who developed ESKD at 36 months were 9.8%, 29.1%, 63.0%, and 83.3%, respectively (P < 0.001). Those belonging to the higher risk groups showed more pronounced proteinuria and anemia at diagnosis (P = 0.001, P < 0.001, respectively). Although our patients exhibited a more severe disease phenotype than those of ANCA renal risk score and AKRiS, both scores performed equally well: The Harrell C-index was similar (0.8381 versus 0.8337). Beyond that, we found differences and similarities in the risk associations between the subgroups of both scores and disease activity or patient outcome, with some of them being described for the first time. For example, there was a higher risk of renal failure with anemia but not with C-reactive protein and the Birmingham Vasculitis Activity Score and an increased incidence of relapsing disease in the lower risk categories of ANCA renal risk score. Conclusions Here, we present the first external AKRiS validation confirming the improved ESKD prediction of the revised score in our cohort. Furthermore, we highlighted associations between risk score categories and patient mortality or vasculitis relapse.