The Anti-Neutrophilic-Cytoplasmic-Antibody-P (ANCA) test is used to detect, aid in the diagnosis of, and sometimes monitor certain forms of the autoimmune disorder systemic vasculitis (inflammation of blood vessels). ANCA are a sensitive and specific marker for ANCA-associated systemic vasculitis. This test can be done when you notice symptoms such as fever, muscle aches, and weight loss that your health practitioner thinks may be due to a vascular autoimmune disorder. The test can also be done when you have symptoms such as intermittent diarrhea and abdominal pain.