Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is the term used for a group of diseases that include granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Patients with ANCA-associated vasculitis may develop antineutrophil cytoplasmic antibodies. Detection of antineutrophil cytoplasmic antibodies is an established diagnostic procedure for assessing patients who may have ANCA-associated vasculitis. Human neutrophils' cytoplasmic granules contain a variety of enzymes, notably: Proteinase 3 (PR3),  Myeloperoxidase (MPO),  Elastase,  Cathepsin G, amongst many others, which ANCA reacts with. The most well-characterised enzymes out of these are PR3-ANCA and MPO-ANCA. Patients with GPA often have autoantibodies against PR3-ANCA, resulting in the cANCA pattern, a distinctive granular cytoplasmic illumination trend on ethanol-fixed neutrophils. MPA Patients are more likely to have antibodies against MPO-ANCA, which cause the perinuclear anti-neutrophil cytoplasmic antibody (p-ANCA) characteristic of perinuclear cytoplasmic excitation on ethanol-fixed neutrophils. EPGA may be inconclusive for ANCA, or it can be p-ANCA positive with reaction to MPO-ANCA. Patients with ulcerative colitis, the most common form of irritable bowel syndrome, may also have the ANCA pattern, typically lacking substantial MPO-ANCA sensitivity. If you exhibit autoimmune vasculitis, your doctor might recommend an ANCA test. These signs include: Fever Fatigue Loss of weight Aches in the joints or muscles Your symptoms may also impact one or more particular organs in your body. Organs that are frequently impacted, and the symptoms they bring on are as follows: Eyes Redness Distorted/absence of vision Ears An earache with ringers (tinnitus) Loss of hearing Sinuses Headache Stuffy nose Nose bleeds Skin Rashes Ulcers Lungs Cough Difficulty breathing Chest pain Kidneys Urine with blood in it Foamy urine Tingling and numbness in various body parts The fluorescence pattern of the cells can be classified as either cytoplasmic (c-ANCA) or perinuclear (p-ANCA). One of the two ANCA testing categories may be used in a laboratory: Indirect Immunofluorescence (IIF) – You can determine if you have autoantibodies or not by receiving a positive or negative result through this test. Enzyme-Linked Immunosorbent Assay (ELISA) – This test aids in locating a specific protein in neutrophils. However, to diagnose GPA, MPA, or EGPA, the indirect immunofluorescence assay should not be the only method used. Any positive ANCA findings must be validated utilising solid-phase immunoassays employing PR3-ANCA (c-ANCA) or MPO-ANCA owing to the absence of clinical specificity.   Medically reviewed by Dr Srikanth M, Haematologist , Apollo Hospitals Cancer Centre Nandanam,Chennai