ANCA antibodies, i.e. anti-neutrophil cytoplasmic antibodies, are not only seen in three diseases. ANCA is closely related to a variety of clinical vasculitis and is also seen in a variety of immune diseases, such as systemic lupus erythematosus and rheumatoid arthritis, and is important in aiding disease diagnosis.1. Vasculitis: mainly seen in ANCA-associated vasculitis, lesions mainly involving small vessels, including microscopic polyangiitis, granulomatous polyangiitis (Wegener’s granulomatosis) and eosinophilic granulomatous polyangiitis, also seen in nodular polyangiitis, etc. Patients with vasculitis usually have fever, joint and muscle pain, malaise and other symptoms, and the affected local skin can also show erythema, papules, necrosis, ulcers and other degrees of damage, and can also involve the lungs, kidneys and eyes, ears, nose and throat, and can often show positive ANCA antibodies after examination. The disease may aggravate and lead to different degrees of damage to the heart, kidneys, nerves, etc. There may be positive ANCA antibodies, and anti-nuclear antibodies, anti-dsDNA antibodies and antiphospholipid antibodies may also be detected; 3. Rheumatoid arthritis: It may lead to morning stiffness, joint deformity and other symptoms, and as the disease aggravates, it may affect the locomotor system and respiratory system, etc. There may be positive ANCA antibodies. ANCA antibody positivity, rheumatoid factor and anti-citrullinated protein antibodies are also important detection indicators; 4, other: ANCA antibody positivity can also be seen in primary focal segmental necrotizing glomerulonephritis, acute glomerulonephritis, chronic inflammatory bowel disease, autoimmune liver disease and lung inflammatory diseases, in order to identify the cause, further relevant tests are required.