Is thrombosis prevention necessary on flights?

Photo of women on an airplane
PantherMedia / Jean-Marie Guyon

The risk of deep vein thrombosis (DVT) is very low in healthy airline passengers. People who have a higher risk of thrombosis can wear compression stockings for prevention, though.

Deep vein thrombosis (DVT) occurs when a blood clot forms in a person’s veins. Long flights can increase the risk of thrombosis because you hardly move your legs during the journey. But most blood clots are small, go unnoticed and then dissolve on their own.

Deep vein thrombosis is generally very rare during long flights: Studies have shown that only about 2 out of 10,000 people develop thrombosis with noticeable symptoms on flights lasting longer than four hours. They found that the risk is greater on longer flights. It is still not clear whether having a seat with more legroom affects the risk of developing thrombosis.

Research on wearing compression stockings on flights

Researchers from the looked at whether wearing knee-high compression stockings can lower the risk of DVT while traveling by plane. They analyzed the results of nine comparative studies involving 2,600 airline passengers. Half of the passengers wore compression stockings, while the other half didn't. In most cases ultrasound scans were done after the flight to see whether any blood clots had formed.

The compression stockings used in the studies were made by various manufacturers. They were knee-high and the pressure they applied ranged between 15 and 30 mmHg (compression class 1 or 2). The participants were asked to start wearing the stockings at least two hours before the flight. The flights lasted between 7 and 15 hours. Most of the people in the studies had a low risk of thrombosis.

What they found

None of the people in the studies developed deep vein thrombosis that caused noticeable symptoms. But the ultrasound scans that were done after the flights revealed that some passengers had DVT without any symptoms. It was found that the compression stockings had greatly lowered the risk of this kind of thrombosis:

  • Without compression stockings, 22 out of 1,000 passengers developed a symptomless DVT while traveling.
  • With compression stockings, 2 out of 1,000 passengers developed a symptomless DVT while traveling.

In other words, the compression stockings prevented blood clots in 20 out of 1,000 airline passengers.

The studies also showed that passengers who wore compression stockings had less swelling in their legs.

When are compression stockings recommended?

The risk of developing deep vein thrombosis that causes health problems on long-haul flights is very low – especially in people who don't have any risk factors for thrombosis. Whether or not you would like to further reduce this risk by wearing compression stockings is a matter of personal choice.

German and international medical associations generally don't see any reason to wear compression stockings on long-haul flights. But they consider them to be a good option for people who have particular risk factors and would like to do anything they can to prevent DVT. For instance, the risk is higher in people who have cancer or those who have had a DVT in the past.

What else can you do?

People are also advised to do the following things to lower their risk of developing DVT while traveling:

  • Get up and walk around as often as possible during the flight
  • Do exercises that use your calf muscles, such as wiggling your feet
  • Try to reserve an aisle seat so you have more freedom to move
  • Drink enough fluids
  • Wear comfortable, loose-fitting clothing

Arbeitsgemeinschaft der Wissenschaftlichen Medizinischen Fachgesellschaften (AWMF). S3-Leitlinie Prophylaxe der venösen Thromboembolie (VTE). October 2015. (AWMF-Leitlinien; Volume 003 - 001).

Chandra D, Parisini E, Mozaffarian D. Meta-analysis: travel and risk for venous thromboembolism. Ann Intern Med 2009; 151(3): 180-190.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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Updated on May 20, 2021
Next planned update: 2024

Authors/Publishers:

Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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