Pathophysiology of thrombophilic states.

The coagulation system can be considered as a balance in which clotting and fibrinolysis have to be in a state of equilibrium. Increased fibrin formation or decreased fibrinolysis can predispose to thromboembolic diseases. Derailments in the clotting system leading to thrombosis center around the regulatory mechanisms, antithrombin III, protein C, protein S and possibly heparin cofactor II. Many cases of congenital or acquired deficiencies or abnormalities or antithrombin III, protein C and S have been described, all predisposing to thrombotic events. Alterations of the fibrinolytic system can also be associated with thromboembolisms. In particular, abnormalities of plasminogen, tissue plasminogen activator release and elevated tissue plasminogen activator inhibitor levels seem to be associated with thromboses. Conceivably also factor XIIa (Hageman factor) and prekallikrein deficiencies, when associated with thrombosis, exert their mechanism through the fibrinolytic system. Finally, about 50% of patients with lupus anticoagulant seem to suffer from thromboembolic disorders. The pathophysiology of this particular association is not known with certainty. Undoubtedly, there will be more disturbances discovered in the hemostasis system that are associated with increased intravascular fibrin formation. The understanding of these derailments is at this time only in its earliest stages of development.