Identification of high thrombotic risk triple-positive antiphospholipid syndrome patients is dependent on anti-cardiolipin and anti-beta 2glycoprotein I antibody detection assays

Background The antiphospholipid syndrome (APS) is characterized by thrombosis and/or pregnancy morbidity with the persistent presence of antiphospholipid antibodies (aPL). Triple-positivity (i.e. positivity for lupus anticoagulant [LAC], anti-cardiolipin [aCL] and anti-2glycoprotein I [a2GPI] antibodies) is associated with a high thrombotic risk. Objectives We investigated the variability in triple-positivity detection by measuring the same samples with four commercially available solid phase assays. In addition, the added clinical value of aPL in LAC-positive patients was investigated, as well as the association of IgM triple-positivity and thrombosis. Patients/Methods We included 851 patients from seven European medical centers. Anti-CL and a2GPI IgG/IgM antibodies were determined by four platforms: BioPlex((R))2200, ImmunoCap((R))EliA, ACL AcuStar((R)) and QUANTA Lite ELISA((R)). Results Triple-positivity detection by solid phase assays varied, ranging from 89 up to 118 in thrombotic APS patients (n = 258), of which 86 were detected independent of the platform. Lupus anticoagulant positivity resulted in an odds ratio (OR) for thrombosis of 3.4; triple-positivity (irrespective of the isotype) increased the OR from 4.3 up to 5.2, dependent on the platform. Triple-positivity solely for the IgM isotype did not increase the OR for thrombosis compared with LAC positivity. The highest OR for thrombosis was reached for positivity for IgG and IgM a2GPI and aCL (8.6 up to 28.9). Conclusions Triple-positivity proved to be highly associated with thrombosis, but identification is assay dependent. Within triple-positivity, IgM antibodies only have an added clinical value in patients positive for IgG antibodies.