Long flights and blood clot risk when you have cancer

Call 911 for sudden unexplained shortness of breath, chest pain that is worse when you breathe in or cough, coughing up blood, or fainting. CDC names these among the most common signs of acute pulmonary embolism — a clot in the lungs. On an aircraft, tell the cabin crew immediately rather than waiting for landing.

Seek medical care the same day for pain or tenderness, swelling, warmth, or redness or discolouration in a leg or arm. CDC lists these as typical signs of deep vein thrombosis in the limbs. Do not walk it off or wait to see whether it settles overnight.

This question comes up a lot because cancer and long flights each raise clot risk on their own. People in treatment often need to travel anyway.

CDC says long trips are a risk by themselves: "Extended periods of limited mobility are inherent to long-distance travel and can increase a traveler's risk for VTE." VTE is the umbrella term for clots in the veins.

CDC is just as direct about cancer: "Cancer patients, especially those who are receiving chemotherapy, have a much higher risk of DVT than other people." Risk is highest for people with brain, pancreatic, stomach, and lung cancers.

Active cancer is on CDC's list of risk factors for travel clots. Other factors on that list include estrogen use, recent hospital stay, surgery or injury, limited mobility, obesity, older age, pregnancy, past clots, thrombophilia, and family history.

It helps to see the scale. CDC cites two studies of flights longer than four hours. One found a risk of about 1 in 4,656 person-flights. The other found about 1 in 6,000 person-flights.

These are small numbers. They also describe travellers in general, not people with cancer specifically. CDC does not give a separate number just for cancer patients, so this article will not guess one.

In plain terms: this risk is worth taking seriously and preparing for. It is not a reason to assume the worst about one trip.

CDC's cancer guidance names more contributors. An injury to a vein during major surgery. Slow blood flow, which happens from staying in bed a long time. Having a catheter in a central vein — common for people in cancer treatment. Older age and obesity add to the risk too.

Several of these travel with you. If you fly a few weeks after surgery with a central line still in place, your risk looks different from a healthy traveller on the same flight.

Before a long trip, ask your team to look at your own mix of risk factors, not just the general advice.

CDC keeps its travel advice simple and practical: "Recommending frequent ambulation and calf muscle exercises for long-distance travelers is reasonable." It also suggests using aisle seats and properly fitted compression stockings.

In plain words, this means get up and walk when you can. Work your calf muscles in your seat when you cannot get up. Choose a seat that makes moving easy instead of awkward. On an overnight flight, an aisle seat can be the difference between moving three times and not moving at all.

CDC makes one point worth remembering: "about half of people with DVT have no symptoms at all."

So a normal-looking leg does not rule anything out. Watch for swelling, pain, tenderness, or red skin in a limb. For a clot that has reached the lungs, watch for trouble breathing, a fast or irregular heartbeat, chest pain that worsens with coughing, coughing up blood, or low blood pressure with fainting.

CDC's cancer guidance suggests asking your doctor about medicine to lower your risk of a blood clot before surgery or catheter placement. A long trip is a similar moment to ask the same question.

This is a short conversation, and it is worth having early. That way, the trip can still be planned around the answer.