DVT and Blood Clot Risk for Cancer Travellers: Prevention Guide
Deep vein thrombosis (DVT) — the formation of blood clots in deep veins, usually in the legs — is a serious but largely preventable condition. For cancer patients, the risk is significantly elevated compared with the general population, and flying adds further risk. Understanding this and taking preventive action is one of the most important things a cancer traveller can do.
Cancer is a well-established risk factor for DVT and its more dangerous complication, pulmonary embolism (PE — a clot in the lungs). The relationship between cancer and clotting (called Trousseau syndrome or cancer-associated thrombosis) is caused by multiple mechanisms:
- Cancer cells release procoagulant substances that activate the clotting cascade
- Chemotherapy damages blood vessel walls and alters clotting factor levels
- Immobility during illness reduces blood flow through leg veins
- Central venous catheters (ports, PICC lines) create turbulent blood flow that promotes clotting
- Hormone therapies (tamoxifen, oestrogen-containing medications) increase clotting risk
- Certain cancers carry particularly high risk: pancreatic, brain, lung, ovarian, and stomach cancers are associated with the highest DVT rates
Research shows that cancer patients face a 4–7 times higher risk of DVT than people without cancer. This risk is highest in the first 3–6 months after diagnosis and during active chemotherapy.
The Flight-DVT Link
Long-haul flights compound cancer-related DVT risk for several reasons:
- Prolonged sitting: Blood pools in the lower legs, slowing venous return
- Dehydration: Dry cabin air and reduced fluid intake thicken the blood
- Reduced cabin pressure: Slightly lower oxygen levels may affect blood flow
- Immobility: Window seats and sleeping passengers make it difficult to move regularly
The combination of cancer and a long-haul flight represents the highest DVT risk category for travellers.
Recognising DVT
Know the symptoms of DVT so you can seek help promptly if they occur:
In the leg (DVT): - Calf or thigh pain or tenderness - Swelling in one leg (asymmetric swelling is a red flag) - Redness, warmth, or discolouration of the skin - Aching, cramping, or heaviness in the leg
In the lungs (pulmonary embolism — emergency): - Sudden shortness of breath (can occur at rest) - Chest pain (sharp, may worsen with breathing) - Rapid heart rate - Coughing up blood - Feeling faint or losing consciousness
If you develop symptoms of pulmonary embolism at any time — on the plane, in transit, or after arrival — this is a medical emergency. Call the cabin crew (on plane) or emergency services (111 in NZ, local equivalents overseas) immediately.
DVT Prevention: The Complete Checklist
Before you fly — see your GP or oncologist: - [ ] Discuss your DVT risk level based on your specific cancer and treatment - [ ] Ask whether prophylactic anticoagulation (LMWH injection) is recommended - [ ] Get compression stockings measured and fitted (medical grade, 30–40 mmHg for high-risk travellers) - [ ] Ask about recent D-dimer levels if you have had a previous DVT
At the airport and during the flight: - [ ] Wear your compression stockings (put on before leaving home, not at the airport) - [ ] Stay well hydrated — drink at least 250 ml of water per hour of flight - [ ] Avoid excess alcohol and caffeine (diuretics that increase dehydration) - [ ] Book an aisle seat to facilitate movement - [ ] Get up and walk to the bathroom every 1–2 hours - [ ] While seated: ankle circles 20 times every 30–60 minutes, calf raises while seated, press heels into floor
In-seat exercises (do every 30–60 minutes): 1. Ankle circles: Rotate both feet clockwise, then anticlockwise, 10 times each direction 2. Foot pumps: Press toes down then pull them up, 20 repetitions 3. Knee lifts: Lift each knee slowly toward your chest, hold 5 seconds 4. Calf raises: Press your toes down firmly into the floor while seated, hold for 5 seconds
After landing: - [ ] Continue wearing compression stockings until you have walked around and your legs have been active - [ ] Stay active on arrival — don't head straight to a hotel room to sleep if possible - [ ] Watch for DVT symptoms in the 72 hours after a long flight (clots can form during the flight but symptoms appear later)
See a doctor urgently if you develop: - One leg significantly more swollen than the other after a flight - Unexplained calf pain or tenderness that doesn't improve with movement - Any symptoms of pulmonary embolism (breathlessness, chest pain, fast heart rate)
Don't wait until you return to New Zealand. DVT and PE require urgent treatment with anticoagulants — delayed treatment increases risk of complications.
Anticoagulants and Travel
If you are already on anticoagulant therapy (rivaroxaban/Xarelto, apixaban/Eliquis, enoxaparin/Clexane, warfarin), discuss flying with your haematologist or GP. Your dose may need adjustment, and you will need to carry your medication in your carry-on with a physician's letter.
For warfarin users, time zone changes can affect INR monitoring schedules. Have a plan for INR testing if your trip extends beyond your next scheduled test.
