PRTN3 and vasculitis: Although FIP and polyangiitis cause similar clinical outcomes, the diagnostic and/or prognostic efficacies of serum MPO‐ and PR3‐ANCAs were found to be low, presumably due to their different pathogenesis as the predominant cells are monocytes and only a small number of neutrophils have been reported in FIP vasculitis (Rush et al., 1990).