Venous thrombosis revisited.

Venous thromboembolism (VTE) is a significant cause of morbidity and mortality in hospitalized patients. For many years, stasis in the deep veins of the legs has been recognized as being a necessary but not a sufficient cause of thrombosis. The recent demonstration of the high prevalence of a mutation at Arg506 in the factor V gene ('factor V Leiden') in patients presenting with VTE has emphasized the protective role of activated protein C in neutralizing thrombin, and has highlighted the importance of genetic factors in the pathogenesis of venous thrombosis. For many if not most patients, the prothrombotic stimulus of a surgical operation with the accompanying stasis may be a sufficient cause for VTE if endogenous anticoagulant mechanisms are impaired. In populations with a high prevalence of the FV:Q506 allele there is now a strong case for screening individuals for the mutant gene if they have a personal or family history of VTE, especially before surgery, during pregnancy or before prescribing oral contraceptives.