International travel can mean flights lasting more than 8 hours. This can potentially put you at risk of developing a blood clot in your leg, and that can be quite devastating. During our consultations, we will assess your risk and recommend appropriate preventive action, if necessary. Here’s what you need to know. We’ll refer to the blood clot as a DVT, which is short for deep vein thrombosis, a clot that develops in leg and may break off and travel to the lung, causing a pulmonary embolus, or PE.

First, all travelers should follow two general recommendations to prevent DVT, and those are to avoid dehydration by drinking plenty of non-alcoholic and non-caffeinated beverages and to exercise muscles in the leg by walking up and down the airplane aisle when possible and by exercising the calf muscles periodically while seated. This is done by flexing the foot toward the shin and then pointing the toes away from the shin.

Other preventive measures may need to be taken if you have certain risk factors for DVT. The main two factors to consider when assessing risk of DVT is duration of your flight and your general risk factors for DVT regardless of travel. A comprehensive review of 25 studies of air travel and DVT was published in 2007 and determined that 6 hours seemed to be the flight duration at which there was an increased risk of DVT as compared to flights less than 6 hours, and longer flights of more than 8 hours duration further increased risk over flights of 6-8 hours. However, the authors of this review noted that if a traveler has no other risk factors for DVT, then there is no specific other preventive measure that needs to be taken other than the general recommendations noted above.

The Centers for Disease Control and Prevention (CDC) lists other risk factors for DVT:
Age > 40
Obesity (BMI > 30)
Recent surgery or injury within 3 months of travel
Use of estrogen-containing birth control pills, rings, or patches
Hormone replacement therapy
Travel during pregnancy or within 6 weeks after giving birth
Having a personal or family history of a blood clot
Active cancer or recent cancer treatment
Varicose veins

The more risk factors you have, the higher your risk of DVT with travel. This risk is difficult to quantify and is based more on professional judgment. If you have one or more risk factors, it may be advisable to discuss the situation with your doctor. If more preventive measures are considered necessary, then graduated compression stockings 15-30 mmHg at the ankle have been proven effective in reducing risk and may be appropriate. In cases of very high risk or where compression stockings are not an option, a doctor may prescribe a dose of a blood thinner (low-molecular weight heparin) prior to the flight.

Our consultants can help assess your risk, and we will communicate with your doctor regarding preventive measures that might be necessary.


Philbrick JT, Shumate R, Siadaty MS, Becker DM. Air Travel and Thromboembolism: A Systematic Review. Society of General Internal Medicine 2007; 22:107-114.

Blood Clots and Travel: What You Need to Know. Centers for Disease Control and Prevention.; accessed October 12, 2017.

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