Table 1 Why the distinction between PR3- versus MPO-ANCA-positive (and versus ANCA-negative) vasculitides may be better than that based on the clinical diagnosis (GPA, MPA or EGPA)

● The reported frequencies of ANCA in GPA, MPA and EGPA and their specificities differ: for example, in non-Asian populations, GPA is mainly associated with PR3-ANCA (c-ANCA), and MPA and EGPA with MPO-ANCA (p-ANCA)

● The pathogenic role of MPO-ANCA is supported by in vitro experiments, animal models, and one (isolated) mother-to-inborn case report. The possible pathogenic role of PR3-ANCA is much less established yet

● The monitoring of PR3-ANCA is not a reliable marker of disease activity or predictor of flare, unless, perhaps, in those patients with renal involvement

● Genetic studies demonstrated that the associations with the SNPs of HLA-DP, SERPINA1 and PRTN3 with PR3-ANCA status and HLA-DQ alleles with MPO-ANCA status were stronger than with the diagnosis of GPA or MPA, respectively

● The outcomes of PR3- and MPO-ANCA-positive patients differ and the statistical associations between the ANCA type and renal outcome, mortality or relapse rates are stronger than with the diagnosis (GPA versus MPA)

● The exact place of EGPA in the ANCA-associated vasculitis group is unclear: the most common manifestations of EGPA (asthma, eosinophilia) are very different from those of GPA and MPA; less than 40 % of EGPA patients are ANCA-positive, mainly with MPO-ANCA (p-ANCA). None of the reported animal models of MPO-ANCA-associated vasculitis showed eosinophilic infiltrates as observed in EGPA