Initially, we suspected infection as the cause of the inflammation, but since there were no significant findings on various imaging tests, we suspected autoimmune disease and measured different antibodies by blood tests; since high perinuclear-ANCA titer with a specific anti-myeloperoxidase antibody (MPO) titer of 31.7 units/mL, we suspected ANCA-related vasculitis and performed a renal biopsy. Here, MPO is linked to autoimmune disease.