MPO and anti-neutrophil cytoplasmic antibody-associated vasculitis: ANCA appears to be closely related to ANCA-associated vasculitis, but not all ANCA-associated vasculitis patients have ANCA, and the detection rate of ANCA has been lower than expected: MPO-ANCA in 30~80% of MPA patients and 0~10% of GPA patients [6,7].