Summary
Clots in the deep veins of the leg are linked with long spells of stillness, which means much of the prevention comes down to movement and a clear plan.
Blood clots in the deep veins of the legs, known as deep vein thrombosis or DVT, are more likely when you are not moving much: after an operation, during an illness that keeps you in bed, or on a long trip. Some personal factors raise the risk further. The main ways to lower it are to keep the leg muscles working, drink enough fluids, follow any clot-prevention plan a hospital gives you, and know the warning signs so that a clot is caught early.
What a DVT is and why it matters
Blood is designed to clot when you are injured, but sometimes a clot forms inside a vein without a cut. In the deep veins of the calf or thigh, a clot can block the flow of blood back towards the heart, causing pain and swelling. The bigger concern is that part of the clot can break away and travel to the lungs. This is called a pulmonary embolism and is a medical emergency. Understanding how circulation in the legs works makes it easier to see why stillness plays such a large part.
Who is more at risk
Doctors weigh several factors together. Having one of them does not mean you will develop a clot, but it is worth knowing which apply to you:
- A recent operation, especially on the hips or knees, or a recent stay in hospital
- Long periods of reduced movement, such as after an injury or during illness
- Cancer and some cancer treatments
- Pregnancy and the weeks after giving birth
- Combined hormonal contraception or hormone replacement therapy containing oestrogen
- A previous clot, or a close relative who has had one
- Older age, carrying extra weight and smoking
- Long-distance travel by air, rail or road, especially combined with other factors
Everyday prevention
- Move regularly. Walking and simple calf exercises keep blood flowing through the deep veins.
- Drink enough. Being well hydrated helps, particularly in hot weather and when travelling.
- Avoid tobacco. Smoking is linked with a higher risk of clots as well as other vessel problems.
- Keep an eye on weight and activity. General fitness supports healthy circulation over the long run.
- Ask about your medicines. If you take hormonal contraception or HRT and have other risk factors, talk to your GP or pharmacist about whether your current option still suits you.
On long trips
- Get up when you can. On trains and planes, walk along the aisle every so often. On long drives, plan regular stops to stretch your legs.
- Work your calves while seated. Point and flex your feet, circle your ankles and press your toes into the floor.
- Drink water through the trip. Go easy on alcohol, which can leave you dehydrated and sleeping in one cramped position for hours.
- Wear loose, comfortable clothes. Avoid tight waistbands and socks that dig into the legs.
- Ask before using stockings. Flight or compression stockings help some travellers, but they must be the right type and size and are not suitable for everyone. A pharmacist can advise and measure you.
Around surgery or a hospital stay
Hospitals usually assess each patient's clot risk. Depending on that assessment, you may be given injections, tablets, compression stockings or a device that gently squeezes the legs. If you are sent home with any of these, use them exactly as instructed for the full time stated, and ask what to do if a dose is missed. Getting up and moving as soon as your care team says it is safe also helps. Before you leave, it is reasonable to ask: how long is my risk raised, and who do I call if I notice symptoms?
Warning signs to act on
| Possible clot in the leg (DVT) | Possible clot in the lung (pulmonary embolism) |
|---|---|
| Throbbing or cramping pain in one leg, usually the calf or thigh | Sudden breathlessness |
| Swelling in one leg | Chest or upper back pain, often worse when breathing in |
| Warm skin over the painful area | Coughing up blood |
| Red or darkened skin, which can be harder to see on darker skin | A racing heartbeat, feeling faint or collapsing |
| Get same-day medical advice | Call your local emergency number |
Swelling in both feet after a long day is more often down to gravity than a clot; our guide on why feet swell helps tell the patterns apart. When in doubt about a single swollen, painful leg, though, it is always better to be checked.
Common questions
Should I take aspirin before a long flight?
Do not start any medicine to prevent clots without advice. Aspirin carries its own risks and is not a routine recommendation for travel. If you are worried about your risk, speak to your GP before you go.
Do compression socks prevent clots?
Correctly fitted compression can lower the risk for some people, such as certain travellers and patients after surgery. It is unsuitable for people with some circulation problems in the arteries, so get advice first.
Can a clot happen without any warning signs?
Yes, sometimes. That is why hospitals assess risk in advance and why prevention matters even when you feel well. Regular checks of your general vascular health, such as those described in our article on vascular screening, are part of the wider picture.
Small adjustments
Changes that cost a minute or less
Easy wins that are simple to keep up.
Mark the cuff
A dot of tape on the cuff shows where it sat last time, so the next reading starts the same way.
Tilt the monitor
Lowering the screen slightly lets your eyelids cover more of the eye.
Two cloths, not one
Keep a spare microfibre cloth so a clean one is always ready.
Check your bite
Lips together, teeth apart: a quick reset whenever you notice clenching.
Background reading only; your GP, pharmacist, dentist or optician can speak to your own circumstances.
