Despite their clinical utility and the importance that laboratory tests have in APS diagnosis, probably the most important drawback of such tests is the elevated intra- and inter-laboratory variation. The aim of the present work was to assess the multilaboratory performance of aCL and anti-β the multilaboratory performance of anti-cardiolipin (aCL) and antibeta 2 glycoprotein I antibodies (anti-β2GPI) assays and to assess the interlaboratory and inter-assay variability. Here, we report the most significant results from the Autoimmunity Workshop of the Spanish Society of Immunology (AWSEI). Seventeen sera from patients with antiphospholipid syndrome (APS) and/or probable APS were collected after written informed consent. Thirty-three laboratories participated and measured aCL and anti-anti-β2GPI. 61 and 49 results/serum for IgG/IgM aCL and anti- anti-β2GPI, respectively, were informed with 20 different assays. A high interlaboratory variation was found in quantitative results regardless the method used. Coefficient of variation ranged from 50% to 128% for aCL and from 9% to 200% for anti-anti-β2GPI. A limited consensus (defined as >90% agreement) was observed in semiquantitative results for IgG/IgM aCL and anti-β2GPI: 47%, 65%, 47% and 70%, respectively. In general, there was concordance between aCL and anti-β2GPI, yet 2 of the 17 sera were positive for anti-β2GPI only. In conclusion, interpretation of aCL and anti-β2GPI results from different laboratories may be done only in semiquantitative terms and its real value for clinical diagnosis of APS is still limited. Cut off values must be set in each laboratory.
