Antineutrophil cytoplasmic antibodies (ANCA) are autoantibodies produced by the immune system that mistakenly target and attack specific proteins within neutrophils (a type of white blood cell). ANCA testing detects and measures the amount of these autoantibodies in the blood. Two of the most common ANCAs are the autoantibodies that target the proteins myeloperoxidase (MPO) and proteinase 3 (PR3). These are called pANCAs and cANCAs, respectively. There are two types of ANCA tests: The first type is called Indirect Immunofluorescence (IIF). This uses neutrophils fixed onto a slide. For the test, serum from your blood sample is mixed with the neutrophils on the slide and any ANCAs in the sample attach to the neutrophil proteins. Treatment of the slide with a fluorochrome-stained antibody reacts with any ANCA present. This produces a pattern of fluorescence that can be seen under a microscope. The pattern may be identified as cytoplasmic (cANCA), perinuclear (pANCA), or atypical ANCA (X-ANCA).