Anti-neutrophil cytoplasmic antibodies and their clinical significance.

Anti-neutrophil cytoplasmic antibodies (ANCA) are a group of autoantibodies that cause systemic vascular inflammation by binding to target antigens of neutrophils. These autoantibodies can be found in serum from patients with systemic small-vessel vasculitis and they are considered as a biomarker for ANCA-associated vasculitis (AAV). A conventional screening test to detect ANCA in the serum is indirect immunofluorescence study, and subsequently confirmed by enzyme-linked immunosorbent assay. A positive staining of ANCA can be classified into three main categories based on the staining patterns: cytoplasmic, perinuclear, and atypical. Patients with granulomatosis with polyangiitis (GPA) mostly have a positive cytoplasmic staining pattern (c-ANCA) whilst a perinuclear pattern (p-ANCA) is more common in microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA) patients. Atypical pattern (a-ANCA) is rarely seen in patients with systemic small-vessel vasculitis but it can be found in other conditions. Here, techniques for ANCA detection, ANCA staining patterns and their clinical significances are reviewed.