Clinical Phenotype Identifies Individuals with ANCA-Associated Vasculitis Who Do Not Require Kidney Biopsies for Diagnosis of Kidney Involvement

Background: Kidney involvement is common in ANCA-associated vasculitis (AAV). The most common finding on kidney biopsy in AAV is crescentic glomerulonephritis (GN). Guidelines recommend kidney biopsy in individuals with AAV and kidney abnormalities to confirm kidney involvement. Kidney biopsies are associated with a risk of bleeding and may delay treatment for active AAV. Therefore, identification of characteristics associated with a high likelihood of finding crescentic GN on biopsy can avoid the need for kidney biopsy in these individuals and its associated risks and costs. Methods: We conducted a single-center retrospective cohort study of all individuals with a positive ANCA test and a kidney biopsy between 2000 and 2023 at the Vasculitis and Glomerulonephritis Center at Massachusetts General Hospital. The positive predictive value (PPV) for finding crescentic GN on biopsy based on various clinical findings was evaluated. Results: 142 individuals met the study's inclusion criteria. The median age was 64 and 55% were female. The median serum creatinine was 2.49 mg/dL, and 89% had microscopic hematuria. 73%, 24%, and 3% were positive for antibodies to myeloperoxidase, proteinase 3, or both, respectively. Crescentic GN was found in 85% of biopsies (Fig. 1A). 100% of individuals with ANCA positivity and rapidly progressive GN (defined as ≥50% eGFR loss in ≤6 months, n = 45) had crescentic GN on biopsy. Over 93% of individuals with ANCA positivity, microscopic hematuria, and ≥1 extra-renal system involvement had crescentic GN on biopsy (Fig. 1B). Conclusion: The rate of kidney function decline, microscopic hematuria, and extra-renal symptoms identify individuals with AAV who do not require kidney biopsy to establish kidney involvement. Funding: Veterans Affairs SupportFigure 1. Diagnostic value of ANCA testing for kidney involvement by vasculitis. (A) Kidney biopsy results. (B) Positive predictive value of different clinical presentations.