MPO and autoimmune disease: Levels of myeloperoxidase–anti-neutrophil cytoplasmic antibody (MPO–ANCA), serine proteinase 3–anti-neutrophil cytoplasmic antibody (PR3–ANCA), and complements C3 and C4 were all normal, and the test result for anti-deoxyribonucleic acid (DNA) antibodies was negative, excluding the possibility of autoimmune disease.