Testing and reporting antineutrophil cytoplasmic antibodies (ANCA) in treated vasculitis and non-vasculitic disease

Testing for antineutrophil cytoplasmic antibodies (ANCA) is performed to diagnose or exclude small vessel vasculitis, and, in treated patients, to monitor disease activity. However testing is also undertaken to assist with the diagnosis of other autoimmune diseases and some infections. Most laboratories use the same assays for all sera regardless of the testing indications. The International Consensus Statement on ANCA Testing and Reporting recommended screening for ANCA by indirect immunofluorescence (IIF) and confirming IIF-positive sera in antigen-specific ELISAs for both proteinase 3 (PR3) and myeloperoxidase (MPO). These guidelines have been reviewed after many refinements of the assays, and the development of new testing methodologies. However the advances have focused largely on improving the diagnostic accuracy in new-onset vasculitis, and not on more accurately monitoring disease activity, nor increasing the diagnostic sensitivity for non-vasculitic conditions. The recently-revised guidelines for ANCA testing indicate that where new onset vasculitis is suspected, sera should be examined for both PR3- and MPO-ANCA using any highly sensitive and specific assay, rather than IIF. They further state that where sera are negative in one assay but the suspicion of vasculitis is high, that testing should be repeated using a different assay. The guidelines do not provide recommendations for treated vasculitis or non-vasculitic disease. However for a routine diagnostic laboratory where sera are tested for many different indications, or where the reasons are not known, IIF screening followed by confirmation of IIF-positive sera in antigen-specific assays remains a highly sensitive, specific and convenient method for detecting ANCA in "all-comers".