Air travelers who take long-haul flights are 4 times more likely to develop deep vein thrombosis — a painful blood clot in the veins of the legs — within the first two weeks after their flight, according to researchers in Australia.The investigators linked hospital records of patients with deep vein thrombosis or pulmonary embolism — a life threatening condition that occurs when a blood clot in the legs breaks loose and travels to the lungs - with records on air travel. For the years between 1981 and 1989, they found 153 Australian citizens who were admitted to hospitals with either condition within 100 days of arrival on an international flight. Their results are published in the current issue of the British Medical Journal.
The study shows that 46 blood clot events occurred within 14 days of arrival, and 107 events occurred between 15 and 100 days after arrival. The doctors point out that the patients’ risk of developing a deep vein thrombosis within the first 2 weeks after flying was higher than would be expected of a population that did not travel in an airplane. The risk was not significant in the third week. Therefore, 2 weeks is considered the riskiest time period for developing a deep vein thrombosis after a long-haul flight.
"We found a 12% increase in annual risk for venous thromboembolism for a traveler undertaking one long-haul flight yearly," the researchers write.
But they also point out that the travelers they studied seemed to be healthier than the average population or non-travelers. Therefore, they say the risk for a traveler is lower than the risk to the overall population consisting of travelers and non-airplane travelers.
"We found that around five deaths per year from pulmonary embolism could be attributable to international flights terminating in Australia," the researchers write, "which could correspond to a death rate of 1 per 2 million people arriving."
Earlier this year Britain’s Court of Appeal upheld a ruling that long-distance travelers who develop deep vein thrombosis could not sue airlines for compensation. The challenge was brought by 24 people who either developed thrombosis after a flight or lost family members as the result of a fatal pulmonary embolism. But in that same week a federal court in San Francisco cleared the way for lawsuits against airlines that do not warn passengers about the risks of developing a potentially fatal clot.
The researchers of this study say that although the average risk of developing a deep vein thrombosis is small, prospective passengers with underlying medical conditions that increase their risk of clotting are likely to have a higher than average risk. The doctors say airlines and health authorities should continue advising passengers on ways to minimize that risk.
Doctors recommend that passengers get up and walk during a long flight to keep blood circulating in the legs. It’s when blood is stagnant that a clot is likely to form.
