The Anti-Neutrophilic Cytoplasmic Antibody (ANCA) – C test detects antibodies against proteins found in the cytoplasm of neutrophils (a type of white blood cell). The “C” refers to the type of ANCA antibodies directed against the enzyme myeloperoxidase (MPO), which are commonly associated with vasculitis, a group of autoimmune diseases causing inflammation of blood vessels. Elevated levels of ANCA-C are often seen in conditions like granulomatosis with polyangiitis (GPA) and microscopic polyangiitis. This test helps diagnose and monitor these conditions. A blood sample is required for this test.