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Deep vein thrombosis (DVT)

Expert reviewer, Mr Alok Tiwari, Consultant Vascular and Endovascular Surgeon
Next review due April 2025

Deep vein thrombosis (DVT) is a blood clot that forms in one of your deep veins. This is usually one of the large veins in your leg.

About DVT

Deep vein thrombosis (DVT) can form in any of your deep veins. Deep veins are large veins that are deep inside your body rather than close to the surface of your skin. You’re most likely to get DVT in one of your legs, but you can also get DVT in your pelvis, your arms or your abdomen (tummy).

Normally, blood flows quickly through your deep veins, helped by the action of your muscles on your veins. But if something happens to slow down the blood flow or make your blood more likely to clot, a DVT can form. The DVT may then completely or partly block blood flow in your vein, leading to pain, swelling and other symptoms. For more information on these symptoms, see our section: DVT symptoms below.

A DVT can be dangerous because it can travel to your lungs and block a blood vessel there (this is called a pulmonary embolism). This can be life-threatening. See our section on complications below for more information. Treatment for DVT can help prevent a pulmonary embolism occurring.

DVT causes

Sometimes there’s no obvious reason why you may develop deep vein thrombosis (DVT). But it’s usually down to one or more of the following issues.

  • something causes blood to slow and pool in your veins – this is most likely if you’re immobile (unable to move around) for a long period of time
  • anything that triggers the blood-clotting process
  • damage to your veins

Some of the most common risk factors associated with developing DVT include:

  • having an illness, injury or disability that makes you immobile
  • surgery – you might be immobile for a long period due to surgery itself or you may have a long recovery period afterwards
  • going on a long journey (for four hours or more), especially if you’re flying
  • pregnancy and the period after pregnancy
  • taking treatments that contain hormones – for example, the contraceptive pill and hormone replacement therapy (HRT)
  • damage to your blood vessels from an injury or operation – for example, if you’ve had a catheter (a thin tube) in a vein
  • being dehydrated (not getting enough fluid)

You’re also at greater risk of developing a DVT if you:

  • have had DVT before
  • have a family history of DVT
  • are over 60
  • smoke
  • are very overweight or obese
  • have certain conditions that affect your blood clotting – for example, antiphospholipid syndrome
  • have cancer
  • have other medical illnesses such as infections or inflammatory conditions

DVT symptoms

You may not have any symptoms at all if you have deep vein thrombosis (DVT). Some people only find out they have it because it progresses to pulmonary embolism. But if you do have symptoms, they may include:

  • swelling in your calf (lower leg) or thigh – it’s unlikely that your whole leg will be swollen
  • pain (often a throbbing pain that’s worse when you put weight on it) and tenderness in your leg
  • your skin may feel warm and look red or occasionally purple
  • the veins on your leg may look swollen or bulging

These can often be symptoms of other problems too. But if you have any of these symptoms, seek urgent medical help. This may through a GP, your hospital if you’ve been in for a procedure, or by contacting NHS 111. This is particularly important if you have any of the risk factors listed above – for example, if you’re pregnant, have cancer or have recently had major surgery.

DVT diagnosis

Your doctor or nurse will ask about your symptoms and medical history. They’ll also want to examine you. They’ll assess how likely you are to have a deep vein thrombosis (DVT), based on all your symptoms and risk factors. Your doctor may also recommend some tests to confirm your diagnosis. These may include the following.

  • A leg vein ultrasound, which is sometimes called a duplex ultrasound. This uses sound waves to look at the blood flow through the blood vessels in your leg.
  • A blood test called a D-dimer. This measures a substance in your blood that’s linked to blood clots.

If your doctor or nurse thinks it’s likely you have a DVT, they may recommend starting treatment before your diagnosis is confirmed.

DVT treatment

If you have a deep vein thrombosis (DVT), your doctor will recommend starting treatment straight away. Treatment for DVT aims to stop the clot getting bigger and causing complications such as a pulmonary embolism. But it can also reduce your risk of getting another DVT. You won’t usually need treatment to get rid of the existing clot. Your body should do this by itself.

You can usually stay at home to have your DVT treatment. But you may need to be admitted to hospital if you have any complications or certain problems that put you at higher risk.

Anticoagulants

The main treatment for DVT is a type of medicine called an anticoagulant. Anticoagulants prevent the existing clot getting bigger and new blood clots forming. You’ll usually need to keep taking them for at least 3 to 6 months. But depending on what’s caused your DVT, your doctor may recommend continuing to take them for the long term.

There are two main types of anticoagulant treatment used for DVT.

  • Warfarin. You’ll need to have regular blood tests (called INR tests) if you’re taking warfarin. This is to make sure your blood is clotting properly.
  • Direct oral anticoagulants (DOACs) such as apixaban, edoxaban and rivaroxaban. These are newer medicines. If you are taking these medicines, you don’t need to be monitored as closely as with warfarin. But they’re not suitable for everyone.

Sometimes you may also need to have injections of a medicine called heparin. If you’re taking warfarin, you’ll need to have heparin injections for the first five days, while the warfarin starts to work. You may also need heparin injections before starting certain DOACs.

The main side-effect of taking anticoagulant medicines is excessive bleeding. This can include nosebleeds, bruising, bleeding gums, blood in your wee or poo, and bleeding more than normal if you cut yourself. If you’re taking anticoagulants, your doctor should give you an anticoagulant information booklet and an alert card, which you should always carry with you. The card lets other health professionals know that you’re taking these medicines. This is important in case of an emergency or before you have any other treatment.

Inferior vena cava filters

Most people with DVT can have treatment with anticoagulants. But if you can’t or it doesn’t work, your doctor may suggest you try treatment with a device called an inferior vena cava (IVC) filter. An IVC filter is a small metal device. It’s placed inside a vein to trap any clots before they can travel to your heart and lungs. You may also have one if your DVT keeps coming back.

Managing symptoms

Your doctor may make the following suggestions to manage your symptoms of DVT, such as pain and swelling.

  • Start walking again as soon as possible because this can ease your symptoms.
  • Keep your leg raised while you are resting, to reduce swelling and keep it comfortable.
  • If you need pain relief, take paracetamol or co-codamol. You shouldn’t take aspirin or NSAIDs (non-steroidal anti-inflammatory medicines) like ibuprofen when taking anticoagulants. This is because these painkillers can increase the risk of bleeding.
  • You could try compression stockings to help with your symptoms. These are tight stockings that help to keep your blood moving through your leg veins. You can get these stockings from your pharmacy. It’s important to get stockings that fit properly – ask your pharmacist for advice.
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DVT complications

Most of the time, deep vein thrombosis (DVT) doesn’t cause any further problems. But possible complications of DVT include pulmonary embolism and post-thrombotic syndrome.

Pulmonary embolism

A pulmonary embolism happens when a blood vessel in your lungs becomes blocked. If you have a DVT, the blood clot may dislodge or a piece may break off and travel in your bloodstream to your lungs. Here it can get stuck in a blood vessel, causing a pulmonary embolism. A pulmonary embolism can stop blood reaching your lungs properly, causing chest pain and difficulty breathing. This can be fatal if you don’t get treatment quickly.

Post-thrombotic syndrome

This is a set of problems some people develop after a DVT. These can include a painful and swollen leg that can get worse when you walk and sore, dry skin. This syndrome could happen if the damage caused by DVT increases the pressure in your vein. If the condition becomes severe, you could develop an ulcer on your leg and this can be difficult to heal.

DVT prevention

If you're in hospital for surgery or because of illness, your nurse or doctor will recommend certain measures to reduce your risk of deep vein thrombosis (DVT). These may include the following.

  • Making sure you’re drinking enough fluids to stay hydrated. If you’re unable to drink, you’ll be given fluids through a drip.
  • Getting up and starting to move about as soon as you can after an operation or illness.
  • Wearing compression stockings to help increase the blood flow through your veins.
  • Having an injection of an anti-clotting medicine as well as or instead of wearing compression stockings.
  • Using a special device that squeezes against your legs to get the blood in your deep veins moving.

Preventing DVT when travelling

You can also help prevent blood clots from developing during a long journey by doing the following.

  • Get up and walk around whenever you can.
  • Do exercises to stretch your leg muscles when you’re sitting down. This might involve bending and straightening your knees, feet and toes.
  • Drink enough fluid so you don’t become dehydrated, but don’t drink excessive amounts of alcohol.
  • Wear comfortable, loose clothing.

Lower leg exercises to prevent DVT [Animation]

If you’ve already had a DVT, there are lifestyle changes you can make to reduce your risk of getting another one. These include stopping smoking, maintaining a healthy weight and regularly exercising. It’s also important to keep taking any medications you’re prescribed.

Frequently asked questions

  • The pain from deep vein thrombosis (DVT) is often a throbbing pain. This may feel worse when you walk or bear weight on your leg. You may also have other symptoms – like swelling and tenderness. Read our symptoms section above for more information.

  • Signs of a blood clot can include swelling, pain and tenderness in your leg. But sometimes you may only be aware of a blood clot if it causes a pulmonary embolism. This can cause chest pain and difficulty breathing. Seek urgent medical help if you have these symptoms. See our sections on symptoms and complications above for more information.

  • Deep vein thrombosis (DVT) is where a blood clot forms in one of your deep veins. It usually happens in one of the large veins in your leg. You can also get DVT in your pelvis, your arm or your abdomen (tummy).

  • Your risk of having a deep vein thrombosis (DVT) is increased if you’ve already had one. This is particularly true if you have ongoing factors that increase your risk of DVT – for example, having a medical condition or continuing to smoke. If you developed DVT after an injury or operation, your chances of having another one may be less.



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Related information

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    • Pulmonary embolism. NICE Clinical Knowledge Summaries. cks.nice.org.uk, last revised February 2022
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    • Deep vein thrombosis. BMJ Best Practice. bestpractice.bmj.com, last reviewed 16 February 2022
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    • Oral anticoagulants. NICE British National Formulary (BNF). bnf.nice.org.uk, last updated 25 February 2022
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    • Anticoagulant – oral. NICE Clinical Knowledge Summaries. cks.nice.org.uk, last revised August 2021
    • Interactions. Warfarin. NICE British National Formulary (BNF). bnf.nice.org.uk, last updated 25 February 2022
    • Compression stockings. NICE Clinical Knowledge Summaries. cks.nice.org.uk, last revised September 2018
    • Kahn SR. The post-thrombotic syndrome. Hematology. Am Soc Hematol Educ Program. 2016; (1):413–18. doi:10.1182/asheducation-2016.1.413
    • Venous thromboembolism in over-16s: reducing the risk of hospital-acquired deep vein thrombosis or pulmonary embolism. National Institute for Health and Care Excellence (NICE). www.nice.org.uk, last updated 13 August 2019
    • Principles of surgery. Oxford Handbook of Clinical Surgery. Oxford Medicine Online. oxfordmedicine.com, published November 2021
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  • Reviewed by Pippa Coulter, Freelance Health Editor, April 2022
    Expert reviewer, Mr Alok Tiwari, Consultant Vascular and Endovascular Surgeon
    Next review due April 2025

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