Newswise — Most people won't need them — but travelers who pull on a pair of elastic support hose before boarding a long flight can cut their risk of blood clots, according to a new review of research.
The review examined the evidence that compression stockings can prevent deep vein thrombosis. Sometimes called "traveler's thrombosis," DVT is a circulatory condition in which blood coagulates into small clots inside a blood vessel.
Compression stockings — made from elasticized material — provide graduated, gentle pressure and are designed to keep blood flowing properly.
Lead researcher Mike Clarke, Ph.D., and his team uncovered strong evidence that flight stockings work. The review found that compression stockings reduce the risk of symptomless DVT to one to three cases per 1,000 long-haul passengers, down from 10 to 30 cases per 1,000.
"It's an extremely dramatic reduction, but it's of something that in the first place wasn't very common. So these stockings reduce a fairly small risk, to something tiny," said Clarke, director of the United Kingdom Cochrane Centre.
The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates research in all aspects of health care. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing trials on a topic.
Deep vein thrombosis usually causes no symptoms because small clots are easily broken down by the body. But larger clots can block the flow of blood resulting in noticeable problems like ankle swelling or calf pain.
Years ago traveler's thrombosis was dubbed "economy-class syndrome" but researchers say that term is a misnomer because the small risk of thrombosis is present anytime a person is stationary for many hours, be it on a plane or train, in luxury accommodations or in coach quarters.
There is no definitive link between air travel and increased risks for traveler's thrombosis, but some evidence suggests that flights of eight hours or more increase the chances that a person with existing risk factors will develop DVT. The Cochrane reviewers report results from nine studies that examined the effects on travelers who wore compression stockings during flights, lasting seven hours or more. Researchers used special equipment to look for symptomless thrombosis among the study participants. Some passengers were deemed to have a low-to-medium risk of thrombosis while others were higher-risk travelers.
The review gathers data for more than 2,800 passengers. About half of these travelers wore some type of compression stockings, the others did not. The researchers' tests turned up symptomless blood clots in 50 people, just three of those passengers were in the compression stockings group. The other 47 travelers were in the no-stockings group.
The reviewers also found that the stocking-footed passengers reported much less discomfort and swelling in their legs, compared with the travelers who flew without flight stockings.
No one in any of the studies developed a blood clot accompanied by noticeable symptoms, and no one suffered a serious thrombosis-related medical condition.
In very rare instances, DVT complications can be life-threatening. In April 2003, NBC News correspondent David Bloom died of a pulmonary embolism while embedded with U.S. troops in Iraq, when a blood clot blocked an artery to his lung. His family later discovered that the journalist had an inherited blood disorder, which increased his risk for deep vein thrombosis.
Vascular specialist Jack Hirsh, M.D., said before embarking on a long-haul flight people who have had blood clots in the past or a strong family history of thrombosis should consult their doctor and consider using compression stockings or medication therapy to prevent blood clots.
Hirsh, who established a thrombosis research center at McMaster University in Hamilton, Ontario, said people who have had a chronic illness that kept them immobilized also have an elevated risk for blood clots during long-distance air travel.
The reviewed studies did not find any serious safety issues associated with using compression stockings, and Clarke said the risks and costs appear to be moderately low.
"If you put the stockings on and they're not comfortable, you might take them off," Clarke said. "And they've not cost you a vast amount of money either."
A pair of compression stockings cost as little as $16 at the drug-store, but higher-quality socks sell for as much as $60. Most people will do fine buying their compression stockings off-the-rack, said Hirsh, who was not involved in the Cochrane review. But people with skinny, long legs or short, thick legs may need to get their stockings custom fitted.
For the average traveler compression stockings are not a must-have travel-item.
"The risk just really does not justify it," Hirsh said. But he added: "If someone is scared about thrombosis when they take a long flight, it's reasonable to allay their anxiety. If they are prepared to pay the sixty bucks for stockings, by all means wear them."
Clarke M, et al. Compression stockings for preventing deep vein thrombosis in airlines passengers. The Cochrane Database of Systematic Reviews 2006, Issue 2.
The Cochrane Collaboration is an international nonprofit, independent organization that produces and disseminates systematic reviews of health care interventions and promotes the search for evidence in the form of clinical trials and other studies of interventions. Visit http://www.cochrane.org for more information.
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