Revised 2017 international consensus on ANCA testing in small vessel vasculitis: support from an external quality assessment.

We read with great interest the multicentre study of Damoiseaux et al 1–3 on the detection of antineutrophil cytoplasmic antibodies (ANCA). ANCAs are important laboratory markers to support the diagnosis of ANCA-associated small vessel vasculitis (AAV), including granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA). Traditionally, laboratories screen for ANCA by indirect immunofluorescence (IIF) and IIF positive samples are further evaluated for antibodies to proteinase 3 (PR3) or myeloperoxidase (MPO) by specific immunoassays. Such diagnostic algorithm is based on an international consensus statement on ANCA testing issued in 1999.4 Over the last two decades, the diagnostic performance of immunoassays has significantly improved. [...