It can be classified into various clinical disease phenotypes: granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), eosinophilic granulomatosis with polyangiitis (EGPA), and renal-limited AAV or serologic subtypes, which are myeloperoxidase (MPO)-AAV and proteinase 3 (PR3)-AAV. Here, MPO is linked to granulomatosis with polyangiitis.