The systemic vasculitides, which are associated with ANCA, are inflammatory diseases of blood vessels and comprise a heterogeneous group of disorders, the causes of which are generally unknown. The diseases have diverse presentations, and are often rapidly progressive, causing irreversible injury to the vessels of kidney and lungs. The presence of ANCA in patients with vasculitis was first observed by Davies in 1982 (107). ANCA are autoantibodies with specificities for proteins located in the primary and secondary granules of neutrophils and in the peroxidase-positive lysosomes of peripheral blood monocytes. They were originally detected by indirect immunofluorescence on ethanol-fixed neutrophils, producing characteristic staining patterns with accentuation of the fluorescent activity within the nuclear lobes. Two major patterns of immunofluorescent staining have been observed: a classical or cytoplasmic staining, designated cANCA, and a perinuclear pattern, designated pANCA.
Other staining patterns have been described and are generally noted as atypical (108) or snowdrift patterns. The nature of the antigens and clinical significance of the antibodies responsible for these atypical fluorescent patterns is currently unclear (109).

The association between ANCA and Wegener's granulomatosis, a systemic necrotising vasculitides, was formally described by van der Woude in 1985 (110) and confirmed by others (111).

ANCA are autoantibodies which are mostly directed against enzymes located within the primary or azurophil granules of neutrophilic granulocytes

• ANCA = Antineutrophil cytoplasmic autoantibodies
• cANCA = cytoplasmic or classic pattern (antiproteinase 3 antibodies)
• pANCA =  perinuclear pattern (anti myelo peroxidase antibodies)
• aANCA = atypical ANCA