#675 Application of ANCA-associated vasculitis Histopathological Classification and Renal Risk Score for prediction of end-stage kidney disease

Abstract Background and Aims Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease predominantly characterized by inflammation of small-sized blood vessels along with the presence of circulating ANCA. The kidney is frequently involved and, even though immunosuppressive therapy has dramatically improved the outcome of AAV patients, a significant proportion of patients progress to end-stage kidney disease (ESKD). Therefore, establishing and validating tools to predict renal outcomes in patients with AAV is crucial. Here we analyzed the application of two tools in predicting kidney survival in a Portuguese single-center cohort with AAV. Method We conducted a retrospective cohort study at a tertiary-care hospital in Portugal (Hospital de São João, Porto), from December 2010 to June 2023. Patients with a kidney biopsy-proven AAV were included. Serological ANCA-negative patients and patients with overlap syndromes, such as AAV in combination with anti-glomerular basement membrane disease, were excluded. Based on electronic records, information on demographics and clinical variables were collected. Kidney biopsies were reviewed to calculate: Berden histopathological classification and the Brix Renal Risk Score (RRS). Kidney survival was defined as the time from diagnosis to the need for kidney replacement therapy. A Kaplan-Meier analysis was performed to compare kidney survival based on the mentioned classifications. Results Fifty-one patients were enrolled, 78% (n = 40) of whom were positive for myeloperoxidase (MPO). The majority were men (61%, n = 31) with a mean age of 65 (± 12) years and a mean serum creatinine of 4.59 mg/dL (± 2.74) at diagnosis. During a median follow-up of 39 (IQR, 7-84) months, 20 patients (39%) progressed to end-stage kidney disease (ESKD), 10 patients (20%) died with preserved renal function and 21 patients (41%) did not need hemodialysis. Concerning Berden classification, 13 patients with a crescentic class, 4 patients with a mixed class and 3 patients with a sclerotic class developed ESKD. After 48 months of follow-up, renal survival was 100%, 90%, 61% and 26.7% in the focal, mixed, crescentic and sclerotic class groups, respectively. Berden classification did not correlate with kidney survival (p = 0.211). Concerning RRS, 10 patients in the high-risk group and 5 patients in the medium-risk group developed ESKD. After 48 months of follow-up, renal survival was 100% in the low-risk group, 85.7% in the medium-risk group, and 41.6% in the high-risk group. A correlation was established between kidney survival and RRS score (p = 0.003). Conclusion In our cohort RRS was predictive of ESKD, contrary to Berden histopathological classification. The information derived from these risk models strongly add to standard biochemical and clinical data. Patients with higher risk of ESKD need close follow-up and a tailored treatment plan regarding preparation for renal replacement therapy.