Granulomatosis with polyangitis (GPA) is an idiopathic, systemic inflammatory disease characterized by necrotizing granulomatous inflammation and pauci-immune small- vessel vasculitis of upper and lower respiratory tract and kidneys. The discovery of anti-neutrophil cytoplasmic antibodies (ANCAs) as a marker associated with GPA focused attention on the potential pathogenic role of these antibodies. Although it has been described that ANCAs recognise a variety of myeloid antigens, only antibodies that react with proteinase 3 (Pr3) and myeloperoxidase (MPO) have consistently been linked to vasculitis syndromes. Pr3-ANCA is the predominant autoantibody found in patients with GPA. The discovery of ANCA has made the diagnosis of this disease even more possible but there is almost always a need to confirm the diagnosis via histological examination of the lesional tissue.
