Background Since 1988, the European Consensus Finding Study Group on autoantibodies in rheumatic diseases (ECFSG), also known as the EULAR (European League Against Rheumatism) autoantibody study group, has been distributing sera with unspecified antibodies to European laboratories (presently n=43) for evaluation of different autoantibody measurement techniques in a clinical context. Use of international reference standards helps align test results by adopting internationally used measurement units, but there are no standards for many autoantibody specificities. Recently, the scope of ECFSG was expanded to include unbiased autoantibody characterisation of serum/plasma specimens with potential for serving as future autoantibody reference standards.
Materials and methods Four samples were evaluated as tentative international reference standards for four different autoantibody specificities: double stranded/native DNA (dsDNA: 2013/14), IgG anti-beta2 glycoprotein 1 (b2GP1), proteinase 3 (PR3) and myeloperoxidase (MPO; 2015/16). The samples were evaluated ‘blind’ for multiple autoantibody specificities by participating laboratories.
Results All or almost all participating laboratories detected the target specificities, and all samples showed restricted autoantibody specificities related to the target specificity. Anti-dsDNA was detected in the tentative anti-dsDNA standard by all laboratories using Crithidia luciliae, ELISA/EIA, FARR assay or ALBIA, together with a homogenous ANA pattern. Other specificities were restricted to histones, nucleosomes and anti-Ku. All laboratories but one detected IgG anti-b2GP1 and IgG anti-cardiolipin, mostly in high levels, in the tentative IgG anti-b2GP1 reference standard, whereas corresponding IgA and IgM antibodies were absent. All laboratories detected anti-MPO, mostly monospecific and in high levels together with P-ANCA pattern in the anti-MPO reagent. Anti-proteinase 3 and C-ANCA pattern, mostly in high levels/titers were detected by all laboratories in the tentative anti-PR3 reagent,
Conclusions The expanded scope of ECFSG has enabled broad characterisation of new tentative autoantibody reference standards. The anti-dsDNA specimen has been processed by the National Institute for Biological Standards and Control (NIBSC) for consideration as the 2nd WHO anti-dsDNA reference standard. The other materials are basis for certified reference material for IgG anti-myeloperoxidase (ERM-DA476/IFCC), and the candidate reference materials for IgG anti-proteinase 3 (in certification) and for IgG anti-β2PG1 (in evaluation) from the Joint Research Centre of the EU Science Hub.