Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis is the most common cause of rapidly progressive glomerulonephritis worldwide, and the renal biopsy is the gold standard for establishing the diagnosis. Although the prognostic value of the renal biopsy in ANCA-associated glomerulonephritis is widely recognized, there is no consensus regarding its pathologic classification. We present here such a pathologic classification developed by an international working group of renal pathologists. Our classification proposes four general categories of lesions: Focal, crescentic, mixed, and sclerotic. To determine whether these lesions have predictive value for renal outcome, we performed a validation study on 100 biopsies from patients with clinically and histologically confirmed ANCA-associated glomerulonephritis. Two independent pathologists, blinded to patient data, scored all biopsies according to a standardized protocol. Results show that the proposed classification system is of prognostic value for 1- and 5-year renal outcomes. We believe this pathologic classification will aid in the prognostication of patients at the time of diagnosis and facilitate uniform reporting between centers. This classification at some point might also provide means to guide therapy.

Little is known about the anticipated disease course for individuals who present with renal-limited antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis but who lack inflammation on a kidney biopsy. The impact of immunosuppression on renal and overall survival is unknown.Patients were recruited from 2005 to 2016 from 8 centers worldwide (N = 16) for this descriptive study. All had positive ANCA, elevated serum creatinine with active urine sediment, histologic evidence of pauci-immune glomerulonephritis without active lesions, and had no evidence of extrarenal vasculitis. We describe the characteristics of this cohort and the differences in the clinical, histologic, and therapeutic parameters of those who developed primary outcomes of end-stage renal disease (ESRD) and vasculitis relapse.The cohort was 63% Caucasian, and 75% were men, with a median age of 62 years. At entry, the mean ± SD estimated glomerular filtration rate (eGFR) was 24 ± 20 ml/min per 1.73 m, and 5 patients required dialysis. Twelve patients received immunosuppressive therapy, 25% experienced disease relapse, and 38% developed ESRD. Patients who developed ESRD had lower baseline eGFRs (8 ± 5 ml/min per 1.73 m vs. 35 ± 18 ml/min per 1.73 m;  = 0.001) and more often required dialysis at presentation (83% vs. 0%;  = 0.001). Patients who relapsed were less likely to receive immunosuppression (25% for the relapsed group vs. 92% for the nonrelapsed group; relative risk: 0.27, risk difference: 67%;  = 0.03).Among these patients, lower initial eGFR and dialysis dependence at presentation might increase the risk for ESRD. Immunosuppression did not affect renal outcomes in this sample of patients but was associated with a reduced risk for vasculitis relapse. More information is needed on factors that predict treatment response in this high-risk group.