Altered fibrin clot properties and the risk of thromboembolism in women with obstetric antiphospholipid syndrome: a cohort study.

Introduction: Formation of denser and poorly lysable fibrin clots has been reported in thrombotic antiphospholipid syndrome (APS). However, it is not known whether unfavorably altered fibrin clot properties and suppressed fibrinolysis characterize women with obstetric APS (OAPS) free of thromboembolic events (TE).

Objectives: This study sought to investigate fibrin clot characteristics and if they predict TE in OAPS women.  Patients and methods: In 62 women with OAPS and 62 controls plasma fibrin clot properties, i.e., permeability (Ks) and clot lysis time (CLT), along with thrombin activatable fibrinolysis inhibitor (TAFI), plasminogen activator inhibitor-1 (PAI-1), plasminogen, and endogenous thrombin potential (ETP) were determined. During a median follow-up of 54 months, TE were recorded.

Results: OAPS patients had lower Ks (-16.4%) and longer CLT (+16.9%), with slightly higher ETP (+4.2%), TAFI antigen (+15.6%), lower plasminogen (-7.9%) and similar PAI-1 antigen when compared to controls (all P <0.05). High-risk OAPS (n = 47, 75.8%) and lupus anticoagulant (LA)-positive OAPS patients, compared with the low-risk and LA-negative subjects had lower Ks and longer CLT. There were no differences in fibrin clot properties and ETP between single-positive aPL patients and controls. During follow-up higher odds of developing TE were observed in patients with OAPS (adjusted OR = 5.26; 95%CI 1.27-21.87) and OAPS who experienced TE (16.1%, 2.2/year) had lower baseline Ks (-17.5 %) and longer CLT (+12.2, both P <0.05). Reduced Ks (≤6.1x10-9 cm2) predicted TE in OAPS patients.

Conclusions: Prothrombotic fibrin clot properties characterize patients with OAPS, which may increase the risk of TE.