An ANCA (Anti-Neutrophil Cytoplasmic Antibody) test, including cANCA (cytoplasmic), checks for autoantibodies attacking your neutrophils, often indicating autoimmune vasculitis (inflammation of blood vessels) affecting kidneys/lungs; a negative/zero result means no significant antibodies found, suggesting symptoms aren’t from this specific autoimmune issue, while a positive result (often with cANCA/pANCA patterns) means they’re present, requiring further specific testing (PR3, MPO) for diagnosis, though some vasculitis cases have no detectable ANCA