PRTN3 and microscopic polyangiitis: As seropositivity for anti-proteinase 3 (anti-PR3) antibody is associated with worse outcomes in patients with AAV, some authors have proposed a classification system based on serology rather than classical phenotypic differentiation into granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA) [27].