What’s the Risk of Fatal Blood Clots From Flying?

When 28-year-old Emma Christofferson died last October after a 20-hour flight from Australia to London, doctors said her death was caused by a blood clot that had traveled to her lung. When news stories about the case linked the length of the flight to the fatal blood clot, many travelers became concerned: If this could happen to an apparently healthy young woman, what is the risk for older, less healthy airplane passengers? More than a dozen articles on the topic have been published recently in medical journals, and two medical organizations have studied the problem and issued conclusions.

The trouble starts when a small blood clot, or thrombus, forms in the deep veins, usually of the leg--a condition called deep vein thrombosis, or DVT. If the clot travels to the heart and then the lungs, it can kill.

The Aerospace Medical Assn., a Virginia-based organization of aviation medical directors, flight medical officers and other specialists in aerospace medicine, has reviewed the medical literature and thinks the link between air travel and deep vein thrombosis is weak. But it supports doing more studies.

The World Health Organization, after convening a meeting of experts in March, concluded that a link between air travel and lethal blood clots probably exists but is likely to be small. WHO plans to conduct further studies.


Meanwhile, long-haul airplane passengers (and others who must sit for prolonged periods) can take simple precautions to prevent blood clot problems, especially on flights of five hours or more.

“Walk. Exercise your ankles,” says Dr. Russell Rayman, executive director of the Aerospace Medical Assn. Rotating the ankles, even while sitting, can help keep blood circulating. The association also advises passengers to stay well hydrated by drinking plenty of water and avoiding caffeine and alcohol.

It is also wise to do in-seat exercises, including toe lifts (lifting toes and the balls of the feet while heels remain on the floor) and heel lifts, according to the American Physical Therapy Assn.

Some airlines have alerted passengers to the risks and have introduced on-board exercise programs. British Airways has a “well-being” channel among its audio entertainment that talks passengers through in-flight exercises. United Airlines has information about deep vein thrombosis on its Web site, (Under “travel support” on the home page, click on “special needs,” then “health tips.”)


Also a potential complication in hospital and surgical patients, deep vein thrombosis affects more than 2 million people in the United States each year, according to the American Heart Assn. But experts say it’s impossible to estimate the number of cases associated with air travel. The Aerospace Medical Assn. has cited a report published in the medical journal Thorax documenting at least 200 such cases in the past decade.

Researchers are discovering that certain factors put some travelers at greater risk than others. Among them: a family or personal history of the condition, genetic clotting abnormalities, obesity, diabetes, heart disease and cancer. Women who are pregnant or who take oral contraceptives or hormone replacement therapy, people who have had recent surgery, smokers and those over age 40 (or, according to some physicians, 60) are also thought to be at increased risk.

Researchers who evaluated 86 patients who developed deep vein thrombosis within 28 days of flying found that 72% had other risk factors for clotting problems. In their report, published earlier this year in the journal Aviation, Space and Environmental Medicine, they speculated that prolonged sitting on a plane may precipitate the condition if other risk factors are present. The likelihood of developing DVT may be increased for several weeks after a long flight.

Those who have risk factors associated with traveler’s thrombosis should follow the same precautions recommended for other passengers, experts say. They should also check with their doctor about additional measures they can take to minimize risk. Advice varies from physician to physician. Some, among them Dr. Stephen C. Ross, chief of staff at UCLA-Santa Monica Medical Center, advise taking an aspirin the day before the flight to make the blood less likely to clot.

Compression stockings, sold at some pharmacies and online, are also worth considering. These stockings are designed to exert maximum pressure at the ankles, which makes blood less likely to clot in the legs. Ross endorses them for people with risk factors, including anyone with a history of vein inflammation or phlebitis. The Aerospace Medical Assn. includes compression stockings in its list of suggested DVT preventives. Support pantyhose won’t do the job, Ross says: “Support hose will only affect the superficial veins, not the deep veins where the blood clots originate.”

Deep vein thrombosis can arise without warning, or it may be signaled by swelling or tenderness in the calf or other parts of the leg. If the clot reaches the lungs, creating a blockage (pulmonary embolism), symptoms can include chest pain, shortness of breath and fainting. It is vital to seek medical attention for suspected DVT so doctors can administer treatment.


The Healthy Traveler column appears twice a month.