Autoantibodies against phosphatidylserine, prothrombin and phosphatidylserine–prothrombin complex: Identical or distinct diagnostic tools for antiphospholipid syndrome?

BackgroundTo clarify the association and diagnostic utility of measuring antiphosphatidyl serine (aPS), antiprothrombin (aPT) and the antiphosphatidyl serine/prothrombin complex (aPS/PT) antibodies in patients with antiphospholipid syndrome (APS) and recurrent pregnancy loss (RPL).MethodWe measured IgG and IgM anti-aPS/PT (2 different kits) as well as the aPS and aPT autoantibodies by ELISA. All subjects were also tested for the presence of Lupus anticoagulant (LA), IgG and IgM anti-cardiolipin (aCL) and anti-β-2 glycoprotein I (aß2GPI), and these served as the gold standard unless otherwise indicated. Two groups of patients were studied: (i) APS with RPL and/or thrombosis (n = 62); (ii) RPL only (n = 66) and a group of healthy women with successful pregnancies (WSP; n = 30).ResultsThe area under curve (AUC) analyses demonstrated significant differences between the aPS/PT (0.980) and aPT (0.850) assays (p = 0.002) with no significant differences between the 2 aPS/PT kits or the aPS/PT and aPS assays. The overall agreement between the tested aPL antibodies and lupus anticoagulant (LA) for the APS cohort was very poor but associations between aPL assays were substantial (κ > 0.5) as determined by Cohen κ analysis.ConclusionsOur data show a lack of association between aPS/PT antibodies and LA in APS patients with recurrent pregnancy loss. In the evaluation of these patients, there may be redundancy in testing all three markers as the aPT and aPS assays formed part of the aPS/PT antibody repertoire.