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Patients Are Asking: Does Flying Increase My Risk for a Clot
Home is where the heart is, though you might have to travel a long way to get there for the holidays. Long-distance travel may raise your stress level, but can it also raise your risk of getting a blood clot? Dr. Susan Kahn, a Professor of Medicine at McGill University and a Canada Research Chair in venous thromboembolism (VTE), weighs in.
Blood clots affect about 1-2 in 1,000 U.S. adults per year, and the risk may double or triple after a flight that’s 4+ hours. One study estimates that 1 in 4,600 travelers will have a blood clot within 4 weeks of a long flight. According to Dr. Kahn, “the actual risk of a travel-related blood clot is quite small, and the average traveler doesn’t need to worry about it. Billions of people travel by plane every year, and most of them don’t get a blood clot.”
However, those who already have risk factors for a clot may have a higher risk of developing travel-related VTE. These risk factors include:
- Age over 40
- Use of birth control pills or hormone therapy
- Recent injury or surgery
- Limited mobility
- A personal or family history of blood clots
- Active cancer or recent cancer treatment
It’s unclear if long-distance air travel is any riskier than car or train travel, but there are factors unique to airplanes that can affect risk:
- Air travelers sit in tight quarters with the back of the knee pressed against the seat. The vein behind the knee is a common area for clots to form.
- Immobility can raise the risk of a clot, but your seat assignment, turbulence, etc. can make it difficult to move around the plane.
- Your body takes in less oxygen when air pressure is lower, and some data suggest that lower oxygen levels can trigger the body’s clotting response.
- Dehydration may also increase the risk of a clot and drinking coffee or alcohol on a flight can fast-track dehydration.
- Many people sleep on flights – but if you’re sleeping, you aren’t moving or hydrating.
The good news is that there are several commonsense methods that can help lower your risk:
- Choose a bulkhead seat or see if your flight offers extra-legroom seating. If not, avoid putting a bag under the seat in front of you so you have more space for your legs and feet.
- Try to move around the plane every 1-2 hours. Selecting an aisle seat can make it easier to get up and walk.
- Avoid sleeping in awkward positions for long periods of time.
- Try not to cross your legs.
- Avoid wearing tight clothing.
- Drink lots of water and avoid alcohol, caffeine, and sedatives.
- Do some simple exercises in your seat to improve blood flow. (See picture at bottom.)
WHAT DO THE GUIDELINES SAY?
2012 American College of Chest Physicians (ACCP) Guidelines
Low-risk travelers should frequently move, perform calf exercises, and sit in an aisle seat if possible.
It’s suggested that high-risk travelers wear properly fitted, below-knee compression stockings while in flight.
Preventive blood thinners or aspirin are not recommended for long-distance travelers.
2018 American Society of Hematology (ASH) Guidelines
Compression stockings or anticoagulants/aspirin are not recommended for low-risk travelers.
“For the average healthy person taking a long flight, we don’t recommend anything other than commonsense measures, like walking around the plane and staying hydrated,” explains Dr. Kahn, who helped write the guideline.
ASH suggests that high-risk passengers use graduated compression stockings or a preventive dose of low-molecular-weight heparin (LMWH) for flights over 4 hours, If these measures aren’t practical, travelers can consider taking aspirin.
Because there’s still a limited amount of data on travel-related VTE, the ASH recommendations are conditional, meaning that the right course of action may be different for each patient.
The bottom line:
- Travel-related blood clots are rare.
- Moving around and staying hydrated are two ways to stay healthy – both in flight and on the ground.
- Travel-related VTE is an area that needs more research. Clear-cut evidence is lacking.
- Talk to your healthcare provider if you’re concerned about developing a blood clot while traveling.
Blood Clots and Travel: What You Need to Know. Centers for Disease Control and Prevention. https://www.cdc.gov/ncbddd/dvt/travel.html. Updated February 1, 2019.
Kahn SR, et al. Chest. 2012;141(2):e195s-e226s.
Planes, Trains, and VTE. American Society of Hematology Clinical News. https://www. ashclinicalnews.org/features/feature-articles/planes-trains-vtes/. Updated March 1, 2019.
*Originally published in The Beat – December 2019. Read the full newsletter here.