Antineutrophil cytoplasmic antibodies, or ANCA, blood tests detect and diagnose certain forms of autoimmune vasculitis, such as microscopic polyangiitis, and relapses of the conditions, according to Lab Tests Online. ANCA are autoantibodies produced by the immune system that attack proteins in the body's neutrophils, or white blood cell types.
ANCA subsets target the proteins proteinase 3, or PR3, and myeloperoxidase, or MPO, most often. Doctors also use ANCA tests to distinguish between two frequently occurring inflammatory bowel diseases, Crohn's disease and ulcerative colitis, notes Lab Tests Online. Medical professionals typically perform ANCA tests using indirect immunofluorescence microscopy, combining blood samples and neutrophils to allow any existing autoantibodies to react with the cells.