Synergistic Thrombotic Risk of Antibodies Against Phosphatidylserine and Prothrombin and β-2-Glycoprotein I

Background: Coagulation and anticoagulation systems are good targets of antiphospholipid antibodies. We assessed the contribution of the antiphospholipid antibodies to the thrombotic risk. Methods: Enzyme-linked immunosorbent assays on antibodies against phosphatidylserine and prothrombin (PS/PT), protein C, protein S, protein Z, and thrombomodulin were performed in 164 patients who showed positive results for lupus anticoagulant or anticardiolipin antibody. Results: Anti-beta-2-glycoprotein I (beta 2GPI) and anti-PS/PT were significant risk factors for thrombotic events (P < .001, P = .049). However, there was no association between antiprotein C, antiprotein S, antiprotein Z, or antithrombomodulin and thrombosis. Coexistence of anti-beta 2GPI and anti-PS/PT antibodies was significantly associated with thrombotic events (P = .001). Interestingly, the absence of both anti-beta 2GPI and anti-PS/PT antibodies was a significant preventive factor for thrombosis (P = .003). Conclusion: Our data show a lack of association of antiprotein C, antiprotein S, antiprotein Z, and antithrombomodulin antibodies with thrombosis. However, the combination of conventional anti-beta 2GPI with anti-PS/PT antibody is expected to enhance the predicting power of thrombotic risk.