Travel, venous thromboembolism, and thrombophilia.

Current evidence indicates that prolonged air travel predisposes to venous thrombosis and pulmonary embolism. An effect is seen once travel duration exceeds 6 to 9 hours and becomes obvious in long-haul passengers traveling for 12 or more hours. A recent records linkage study found that increase in thrombosis rate among arriving passengers peaked during the first week and was no longer apparent after 2 weeks. Medium- to long-distance travelers have a 2- to 4-fold increase in relative thrombosis risk compared with nontravelers, but the averaged absolute risk is small (approximately one symptomatic event per 2 million arrivals, with a case-fatality rate of approximately 2%) and there is no evidence that thrombosis is more likely in economy class than in business- or first-class passengers. It remains uncertain whether and to what extent thrombosis risk is increased by short-distance air travel or prolonged travel by motorcar, train, or other means. Most travelers who develop venous thrombosis or pulmonary embolism also have one or more other predisposing risk factors that may include older age, obesity, recent injury or surgery, previous thrombosis, venous insufficiency, malignancy, hormonal therapies, or pregnancy. Limited (though theoretically plausible) evidence suggests that factor V Leiden and the prothrombin gene mutation predispose to thrombosis in otherwise healthy travelers. Given that very many passengers with such predispositions do not develop thrombosis, and a lack of prospective studies to link predisposition with disease, it is not now possible to allocate absolute thrombosis risk among intending passengers or to estimate benefit-to-risk ratios or benefit-to-cost ratios for prophylaxis. Randomized comparisons using ultrasound imaging indicate a measurable incidence of subclinical leg vein thrombosis after prolonged air travel, which appears to increase with travel duration and is reduced by graded pressure elastic support stockings. Whether this surrogate outcome measure translates into clinical benefit remains unknown, but support stockings are likely to be more effective and have less adverse effects than the use of aspirin.