Anti-neutrophil cytoplasmic antibodies (ANCA) are a family of autoantibodies 
that react with proteins predominantly expressed in cytoplasmic granules of 
polymorphonuclear neutrophil granulocytes (PMNs). ANCA was initially detected 
using indirect immunofluorescence, allowing for different patterns such as 
p-ANCA (perinuclear) and c-ANCA (cytoplasmic) to be distinguished. Today it is 
common to detect the antibodies by immunochemical assays such as ELISA using 
purified proteins as antigens. The strongest association with ANCA is found in 
the pauci-immune small vessel vasculitides granulomatosis with polyangiitis 
(GPA) and microscopic polyangiitis (MPA). There is compelling evidence that ANCA 
contributes to the pathogenesis in these conditions. ANCA also occurs in 30%-40% 
of patients with eosinophilic granulomatosis with polyangiitis (EGPA) and 
anti-GBM disease, but is uncommon in other forms of vasculitis. ANCA with 
different specificities have been described with varying frequencies in diseases 
such as systemic lupus erythematosus (SLE), rheumatoid arthritis, inflammatory 
bowel disease, endocarditis, chronic infections and hematopoietic malignancies. 
ANCA can also develop as an adverse event during pharmacological treatment. 
These entities are treated quite differently, with therapies ranging from 
immunosuppressive agents over antibiotics to simply removing the causative drug. 
A positive ANCA test thus requires a careful diagnostic work-up.