The discovery of a number of prothrombotic conditions (known generally as thrombophilias) has led to the hypothesis that blood hypercoagulability is the major factor in thrombogenesis. In reality most patients with these conditions are at increased risk when a second thrombogenic factor is operating, e.g., injury, operation, pregnancy, or the contra-ceptive pill. The conditions that are now known to cause thrombophilia include antithrombin deficiency, protein C deficiency, protein S deficiency, activated protein C resistance (Factor V Leiden mutation), and antiphospholipid syndrome. Activated protein C resistance, for example, is present in 5% of the total population, but is found in 20% of those with deep vein thrombosis.
The process of thrombus initiation may be continually occurring on a daily basis as low levels of fibrin degradation products can be measured within all subjects’ blood throughout life. This process is probably overcome by the body’s own natural thrombolytic defenses.
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