Anti-myeloperoxidase (MPO) positivity alone is usually not serious, but if combined with pANCA (anti-neutrophil cytoplasmic) positivity, it is relatively serious, and is mostly caused by autoimmune diseases, such as primary small vessel vasculitis. Anti-myeloperoxidase positivity alone can be caused by a test error, but if it is combined with pANCA positivity, most of the immune diseases, such as primary small vessel vasculitis, are relatively serious. Such diseases cause inflammation and fibrinoid necrosis of the walls of small blood vessels and can affect the kidneys leading to renal failure, which is a relatively more serious disease. Once MPO positive, especially combined with pANCA positive, you need to go to nephrology department as soon as possible to complete other related examinations, if necessary, carry out renal puncture biopsy, determine the cause of the disease and then early treatment!