MPO and anti-neutrophil cytoplasmic antibody-associated vasculitis: Some authors have reported the outcome in 14 patients with very severe renal impairment (eGFR< 20 ml/min/1.73 m2) due to AAV or ANCA negative vasculitis [16]; this multicentre study showed 100% achieving remission and an improvement in kidney function in most of cases (both MPO and PR3 vasculitis).