Antineutrophil cytoplasmic antibodies (ANCA) can occur in patients with small blood vessel vasculitis including granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), or eosinophilic granulomatosis with polyangiitis (EGPA). This assay is useful for evaluating patients suspected of having Autoimmune vasculitis, both Wegeners granulomatosis and Microscopic Polyangiitis.