Antiphospholipid Antibodies, Haemostatic Variables and Thrombosis – A Survey of 144 Patients

Summary Several clotting abnormalities have been put forth to explain the thrombotic tendency of the antiphospholipid syndrome, but a possible role for fibrinogen and von Willebrand factor has been poorly investigated. The present cross-sectional retrospective study evaluated the relationship of IgG anticardiolipin antibodies, lupus anticoagulants, fibrinogen and von Willebrand factor with the occurrence of arterial and venous thromboses in patients with antiphospholipid antibodies. Among the clotting assays for the detection of lupus anticoagulant, dilute Russell’s viper venom time correlated with a history of venous thrombosis more strongly than activated partial thromboplastin time (p <0.0002 vs p <0.009) and was the only test which correlated with a history of arterial thrombosis (p <0.01), also at low levels of IgG anticardiolipin antibodies (p = 0.003). By regression analysis, and after correction for confounders, serum levels of IgG anticardiolipin antibodies were found to be positively associated with the number of venous events (p <0.001). Plasma levels of fibrinogen and von Willebrand factor were associated with each other (p <0.0001; r: 0.48) and with the occurrence of arterial and venous thromboses (p <0.001). Moreover, plasma levels of fibrinogen and von Willebrand factor in thrombotic patients with antiphospholipid antibodies were significantly higher than those of a control group of thrombotic patients who suffered thrombosis for other reasons (p <0.0001 and p = 0.0008 respectively). Titres of IgG anticardiolipin antibodies correlated with plasma levels of von Willebrand factor (p <0.0001; r: 0.42). These findings support the hypothesis that within the antiphospholipid antibody family, subgroups exist which may preferentially associate with arterial or venous occlusions and raise the possibility that elevated plasma levels of fibrinogen and von Willebrand factor may be implicated in the thrombotic tendency of the antiphospholipid syndrome through an involvement of the vascular endothelium, as the relationship between IgG anticardiolipin and von Willebrand factor suggests. Measurement of fibrinogen and von Willebrand factor in prospective studies, besides anticardiolipin antibodies and lupus anticoagulants, may help assess the risk of developing arterial and venous thrombosis in patients with antiphospholipid antibodies.