MPO and microscopic polyangiitis: Of the 44 patients with small to medium-sized vessel vasculitis (GPA, MPA, EGPA, PAN, and unclassified vasculitis), 15 patients (predominantly PAN) were negative for ANCA, 13 patients (exclusively GPA) had ANCA toward PR3 (PR3-AAV), and 14 patients (inclusive of all MPA) had ANCA toward MPO (MPO-AAV).