Evaluation of different immunoassays for the detection of antiphospholipid antibodies: report of a wet workshop during the 13th International Congress on Antiphospholipid Antibodies.

BACKGROUND: The performance and standardization of anticardiolipin (aCL) and anti-β₂ glycoprotein I antibodies (aβ₂GPI) tests for the confirmation of diagnosis of antiphospholipid syndrome (APS) remain a matter of debate and concern. We evaluated the performance of different ELISAs and other new immunoassays for the detection of aCL and aβ₂GPI in a wet workshop at the 13th International Congress on Antiphospholipid Antibodies in Galveston, TX (April 13th, 2010, APLA 2010).

METHODS: Aliquots of 26 un-identified APS or persistently aPL positive serum samples and 21 controls (9 from healthy individuals and 5 from patients with infectious diseases and 7 with various autoimmune diseases) were distributed to all participants/groups. All serum samples were evaluated in various aCL and aβ₂GPI ELISAs, a chemiluminescent immunoassay, a fluoro-enzyme immunoassay, and in a multiplexed immunoassay system. Monoclonal and polyclonal calibrators were also evaluated.

RESULTS: Although not all the assays reported the titers of aCL and aβ₂GPI in the same units, the correlation of positive titers among the assays was good. All aCL and aβ₂GPI tests showed excellent clinical sensitivities, specificities and positive predictive values and good agreement with respect to the levels of the IgG and IgM antibodies, regardless of assay type, or whether tests were done using automated or "manual" systems.

CONCLUSIONS: New methodologies for the detection of aPL look promising and comparable to currently approved ELISA tests. This study provides evidence of progress of efforts of harmonization of tests used to detect aPL.