Tests for antineutrophil cytoplasmic antibodies (ANCA) may be used to: Help detect and diagnose certain forms of autoimmune vasculitis, including granulomatosis with polyangiitis (Wegener granulomatosis), microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis (Churg Strauss syndrome). Sometimes this test may also be used to monitor treatment and/or detect a relapse of these conditions. (For more detailed information on these conditions, see the article on Vasculitis.) Help distinguish between ulcerative colitis (UC) and Crohn disease (CD), two common types of inflammatory bowel disease (IBD). ANCA are autoantibodies produced by a person's immune system that mistakenly attack proteins within the person'sneutrophils (white blood cell types). The most common subsets of ANCA are those that target the proteins myeloperoxidase (MPO) and proteinase 3 (PR3). . The patterns of ANCA seen on Immunofluorescence are. � Perinuclear (pANCA) � most of the fluorescence occurs near the nucleus. About 90% of samples with a pANCA pattern will have MPO antibodies. � Cytoplasmic (cANCA) � the fluorescence occurs throughout the cytoplasm of the cell. About 85% of samples with a cANCA pattern will have PR3 antibodies. � Negative ANCA � very little or no fluorescence If an ANCA test result is positive, then an additional test is performed to determine the amount of antibody present. This is called a titer. To determine the titer, a serum sample is diluted in steps and each dilution is tested for the presence of the antibody. The greatest dilution at which the antibody can be detected is the titer. For example, if a serum tests positive after being diluted 64-fold, the titer is 1:64. The higher the titer, the more antibody is present in the blood. ANCA levels can change over time and may sometimes be used in a general way to monitor disease activity and/or response to therapy; however, titer levels may be inconsistent in some patients, poorly reflecting remission/relapse status. The following table shows results that may be seen in some vasculitis conditions. Condition % of patients with cANCA pattern (PR3 antibodies) % of patients with pANCA pattern (MPO antibodies) Granulomatosis with polyangiitis (Wegener granulomatosis) 90% in active disease, 60-70% no active disease Less than 10% Microscopic polyangiitis 30% 60% Eosinophilic granulomatosis with polyangiitis (Churg Strauss syndrome) Rare 50-80% Polyarteritis nodosa Rare Rare