MPO and granulomatosis with polyangiitis: The AAVs include: granulomatosis with polyangiitis (GPA), most commonly associated with proteinase 3 (PR3)-ANCA, although myeloperoxidase (MPO)-ANCAs are present in a minority; microscopic polyangiitis (MPA), typically associated with MPO-ANCA; single organ disease, including renal-limited vasculitis (again mainly associated with MPO-ANCA); and eosinophilic granulomatous polyangiitis (EGPA) [5].