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 can wear compression stockings for prevention.

Deep vein thrombosis (DVT) occurs when a blood clot forms in a person’s veins. DVT can cause the affected part of the body – usually the lower leg – to feel tender and warm, swell and turn red. But the blood clots often go unnoticed and dissolve on their own again. Long-haul flights can increase the risk of thrombosis if you hardly move your legs during the journey.

Researchers at Harvard University in the U.S. looked for studies on the development of DVT on flights. They found a number of studies on the risk of thrombosis on flights. One large study looked into how common DVT is on journeys lasting longer than four hours.

Thrombosis very rare on long-haul flights

The results of the study suggest that about 2 out of 10,000 people develop thrombosis with noticeable symptoms on flights lasting longer than four hours. The researchers also found out that the risk is greater on longer flights. None of the studies looked into whether DVT is more common in passengers who have seats with less legroom than in passengers with more legroom.

Do compression stockings work?

Researchers from the looked at whether wearing knee-high compression stockings can lower the risk of DVT while traveling. 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 their compression strength (the pressure they applied) ranged between 15 and 30 mmHg. 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.

The outcome

None of the people in the studies developed venous thrombosis that caused noticeable symptoms. But the ultrasound scans that were done after the flights revealed that some passengers had a symptomless DVT. 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 used in these studies prevented blood clots in 20 out of 1,000 airline passengers.

It was also found that the passengers who wore compression stockings had less swelling in their legs. So the stockings helped to prevent fluid retention caused by sitting for a long time.

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 DVT. 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.

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.

Clarke MJ, Broderick C, Hopewell S, Juszczak E, Eisinga A. Compression stockings for preventing deep vein thrombosis in airline passengers. Cochrane Database Syst Rev 2016; (9): CD004002.

Kahn SR, Lim W, Dunn AS, Cushman M, Dentali F, Akl EA et al; American College of Chest Physicians. Prevention of VTE in nonsurgical patients: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012; 141(2 Suppl): e195S-226S.

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. 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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Created on March 23, 2017
Next planned update: 2021


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

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