MPO and vasculitis: AAV is generally classified into microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA), and eosinophilic granulomatosis with polyangiitis (EGPA) but may be categorized according to antigens targeted by ANCA as follows: MPO-ANCA vasculitis, PR3-ANCA vasculitis, and ANCA-negative vasculitis (3, 4).