Diseases & care
Blood clots: deep vein thrombosis and pulmonary embolism
Blood clots that form in the deep veins are a serious but often treatable problem. A clot in a deep vein, usually in the leg, is called a deep vein thrombosis, or DVT. If part of that clot breaks away and travels to the lungs, it causes a pulmonary embolism, or PE, which can be life-threatening. Together these are known as venous thromboembolism. The good news is that clots can be prevented and treated well when spotted early — which is why knowing the warning signs matters. This guide explains how these clots form, who is most at risk, the symptoms to watch for, and how the NHS treats them.
Education and reference only. This article explains how treatments work in plain language — it contains no doses and is not a substitute for advice from your doctor or pharmacist. Always discuss your own treatment with a qualified clinician.
What DVT and PE are
Blood normally flows smoothly around the body, but sometimes it can thicken and form a clot inside a deep vein — most often in the calf or thigh. This is a deep vein thrombosis. The clot can partly block the vein, causing pain and swelling. The bigger danger is if a piece of the clot breaks off and is carried in the bloodstream up to the lungs, where it lodges and blocks blood flow. That is a pulmonary embolism, and it can strain the heart and stop the lungs working properly. Because the two conditions are two ends of the same process, doctors treat prevention and early recognition of both very seriously.
Who is at risk
Several things make a clot more likely, usually by slowing blood flow, damaging a vein, or making blood clot more easily. Being immobile is a big one — after major surgery, during a long hospital stay, when a leg is in a cast, or on very long journeys. Other risk factors include being pregnant or recently having a baby, some contraceptive pills and hormone treatments, cancer and its treatment, being very overweight, older age, smoking, and a family or personal history of clots. Some people inherit conditions that make their blood clot more readily. Often several small risks add up. Knowing your risk matters, because much clot prevention — such as staying mobile and specific hospital measures — is straightforward.
Symptoms to watch for
A DVT usually affects one leg and causes swelling, pain or tenderness (often in the calf), warmth, and sometimes skin that looks red or changed in colour. The whole leg may feel heavy. A pulmonary embolism is more dramatic and dangerous: sudden breathlessness, sharp chest pain that is often worse when breathing in, coughing (sometimes with blood), a fast heartbeat, and feeling faint or collapsing. A PE can happen with or without obvious leg symptoms first. Because a PE can be fatal, these signs are a medical emergency. Anyone with sudden breathlessness or chest pain should call 999, and anyone with a painful, swollen leg should seek urgent same-day medical advice.
How clots are diagnosed and treated
If a clot is suspected, the NHS acts quickly. For a possible DVT, doctors use a scoring system, a blood test called a D-dimer, and an ultrasound scan of the leg. For a suspected PE, they may use a chest scan such as a CT pulmonary angiogram. The main treatment is anticoagulant medicine — often called blood thinners — which stops the clot growing and lets the body break it down over time, while reducing the risk of new clots. Treatment usually lasts at least several months, sometimes longer depending on the cause. In severe, life-threatening PE, stronger clot-busting treatment may be needed in hospital. Compression stockings and staying active also support recovery.
Prevention and recovery
Much can be done to prevent clots, especially around known risk times. In hospital, staff assess everyone's clot risk and may use blood-thinning injections, compression stockings or leg pumps. On long journeys, moving around, doing calf exercises and staying hydrated all help. If you are on blood thinners, taking them exactly as prescribed is vital, and you will be told how to spot signs of bleeding, which is the main side effect to watch for. Most people recover well, though a leg affected by DVT can stay swollen or achy for a while. Follow-up looks at how long treatment should continue and whether any underlying cause needs investigating.
In short
Key takeaways
- A DVT is a blood clot in a deep vein, usually the leg; a PE is when part of that clot travels to the lungs.
- Risk rises with immobility, surgery, long journeys, pregnancy, cancer, some hormone treatments and a family history of clots.
- DVT typically causes a painful, swollen, warm leg; PE causes sudden breathlessness, chest pain and a fast heartbeat.
- Blood thinners are the main treatment, usually for several months, and they stop clots growing while the body clears them.
- Sudden breathlessness or chest pain is an emergency — call 999 — and a painful swollen leg needs same-day medical advice.
Answers
Frequently asked questions
When is a blood clot an emergency?
A pulmonary embolism is an emergency. Call 999 if you or someone else has sudden breathlessness, sharp chest pain that is worse breathing in, coughing up blood, a racing heart, or feels faint or collapses. A painful, swollen, warm leg that could be a DVT needs urgent same-day assessment, as it can lead to a PE.
How can I lower my risk on a long flight?
Move around regularly, flex your calf muscles and wiggle your toes while seated, keep well hydrated, and avoid too much alcohol. If you have extra risk factors, ask your GP or pharmacist about compression stockings before travelling. Most healthy people on short trips are at low risk, but movement helps everyone.
Are blood thinners dangerous?
Anticoagulants are very effective but their main side effect is an increased chance of bleeding. Take them exactly as prescribed, attend any monitoring, and tell your team about unusual bruising, blood in urine or stools, or bleeding that will not stop. The benefit of preventing dangerous clots usually far outweighs the risk when they are managed properly.
Go deeper
Related guides
Sources
Where this is drawn from
- NICE guideline NG158: Venous thromboembolic diseases — diagnosis, management and thrombophilia testing
- NHS — Deep vein thrombosis (DVT) and pulmonary embolism information
- British Society for Haematology — Guidelines on the management of venous thromboembolism
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