Objectives: APS is associated with arterial and venous thrombosis. The unfavourable fibrin clot phenotype, including formation of dense and poorly lysable clots, has been reported in thrombotic APS. We investigated whether abnormal plasma clot properties are predictive of recurrent thromboembolism in APS.
Methods: We followed 126 consecutive patients with thrombotic APS and 105 control subjects, without APS, matched for thrombotic events. Plasma fibrin clot permeability (Ks), turbidity measurements and clot lysis time were evaluated ⩾5 months after a thrombotic event. The primary composite end point was symptomatic recurrent venous thromboembolism, ischaemic stroke and/or myocardial infarction.
Results: During follow-up (median, 62 months; range 46-74 months; 1183.2 patient-years), the primary outcome was observed in 33 (26.2%) APS patients and 16 (15.2%) controls, including 25 (19.8%) and 14 (13.3%) subjects with recurrent venous thromboembolism, respectively. Reduced Ks and prolonged clot lysis time predicted recurrent thromboembolic events in APS patients [per 1 × 10-9 cm2: hazard ratio (HR) = 0.37; 95% CI: 0.24, 0.56; and per 10 min: HR = 1.20; 95% CI: 1.01, 1.40, respectively] and in controls (per 1×10-9 cm2: HR = 0.23; 95% CI: 0.11, 0.42; and per 10 min: HR = 1.51; 95% CI: 1.08, 2.16, respectively). A multivariate analysis showed that positive IgG and IgM anti-β2 glycoprotein I antibodies, withdrawal of anticoagulation, lower platelet count and reduced Ks predicted thromboembolic events in APS patients.
Conclusion: Formation of denser fibrin networks could be a novel risk factor for recurrent thromboembolism in APS, which highlights the importance of fibrin phenotype in thrombotic disorders.