Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a heterogeneous group of small vasculitis of unknown etiology, characterized by the presence of proteinase 3 (PR3) and myeloperoxidase (MPO) in the serum (Kitching et al., 2020). Here, MPO is linked to anti-neutrophil cytoplasmic antibody-associated vasculitis.