3. ANCA positivity or confirmatory histology or both (appendix 5). ANCA positivity requires a typical CANCA pattern by indirect immunofluorescence (IIF), (preferably confirmed by anti-PR3 ELISA), or the presence of PR3-ANCA or MPO-ANCA determined by ELISA, PANCA requires confirmation by anti-MPO ELISA [6]. (Central review of ANCA serology and histology will be performed).