MPO and granulomatosis with polyangiitis: AAV includes microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA), eosinophilic granulomatosis with polyangiitis (EGPA), renal-limited AAV, and certain drug-induced vasculitis syndromes which may be ANCA specific for either myeloperoxidase (MPO-ANCA) or proteinase 3 (PR3-ANCA) [1].