Travel and venous thrombosis.

Debate continues about whether and to what extent travel predisposes to venous thrombosis and pulmonary embolism (PE). Almost certainly, the strength of any association was greatly exaggerated in recent press reports. Conclusions from case-control studies vary, with some finding no excess of recent travel among patients with venous thromboembolism and others reporting a two-four fold excess. The strongest evidence that prolonged air travel predisposes to thrombosis comes from the travel history of people who present with PE immediately after landing. Two independent analyses suggest that the risk of early embolism increases exponentially with travel times beyond 6 hours and may reach 1:200,000 passengers traveling for more than 12 hours. The most likely explanation is venous stasis in the legs from prolonged sitting, and there is evidence (preliminary and controversial) that elastic support stockings may prevent deep vein thrombosis in people who travel long-distances. There is an urgent need for more and better studies to define the absolute hazard from travel-related thrombosis and the personal risk factors that may contribute. Without these, it is difficult to give a balanced account to people who intend to travel or to consider definitive prevention trials. Case reports suggest that in most cases, travel-related thrombosis has affected people who were also at risk because of previous thrombosis, recent injury, or other predispositions. This makes it sensible to target such "at risk" people with advice about hazards and precautions, at least until formal study validates some other approach.