Compared with sera from patients with PTU-induced MPO-ANCA but without clinical vasculitis, sera from PTU-induced AAV patients showed significantly higher reactivity against the H1 fragment of MPO [OD values: 0.17(0.10 to 0.35) versus 0.10(0.04 to 0.21), P = 0.038] (Figure 2). Here, MPO is linked to anti-neutrophil cytoplasmic antibody-associated vasculitis.