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Deep vein thrombosis (DVT)

Published by Bupa's health information team, June 2009.

This factsheet is for people who have deep vein thrombosis (DVT), or who would like information about it.

Deep vein thrombosis (DVT) is a condition in which a blood clot forms in one of your deep veins, usually in your leg. DVT can cause pain and swelling and may lead to complications such as pulmonary embolism.

Animation - How deep vein thrombosis forms
About DVT
Symptoms of DVT
Complications of DVT
Causes of DVT
Diagnosis of DVT
Treatment of DVT
Prevention of DVT
Questions and answers
Related topics
Further information
Sources

How deep vein thrombosis forms

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About DVT

DVT happens when a blood clot forms in a deep vein. DVT is most common in the deep veins of your lower leg (calf), and can spread up to the veins in your thigh. DVT can also first develop in the deep veins in your thigh and, more rarely, in other deep veins, such as the ones in your arm.

Deep veins pass through the centre of your leg and are surrounded by a layer of muscle (see diagram).

When blood clots form in the superficial veins, which lie just under your skin, the condition is known as superficial thrombophlebitis. These superficial blood clots are different to DVT and are much less serious.

Illustration showing a blood clot in the deep vein of the calf which causes deep vein thrombosis
A blood clot in the deep vein of the calf which causes deep vein thrombosis

Symptoms of DVT

Many blood clots that cause DVT are small and don't produce any symptoms. Your body will usually be able to gradually break them down with no long-term effects.

Larger clots can partly or completely block the blood flow in your vein and cause symptoms such as:

swelling of the affected leg
pain and tenderness in the affected leg - you may also find it difficult to stand properly with your full weight on the affected leg
a change in the colour of your skin, for example, redness
skin that feels warm or hot to the touch

Although not necessarily a result of DVT, if you have these symptoms you should visit your GP.

Complications of DVT

DVT may not cause you any further problems, but possible complications can include the following.

Pulmonary embolism

This is the most serious complication of DVT. A pulmonary embolism happens when a piece of the blood clot from a DVT breaks off and travels through your bloodstream to your lungs, where it blocks one of the blood vessels in your lungs. This is serious and in severe cases, can be fatal. See Related topics for further information.

Post thrombotic syndrome

This is something that happens if DVT damages the valves in your deep veins, so that instead of flowing upwards, the blood pools in your lower leg. This can eventually lead to long-term pain, swelling and, in severe cases, ulcers on your leg.

Limb ischaemia

This is a rare complication that only happens in a very extensive DVT. Because of the blood clot, the pressure in your vein can become very high. This can block the flow of blood through your arteries, so less oxygen is carried to the affected leg. This can be painful and lead to skin ulcers, infection and even gangrene.

Causes of DVT

You are more likely to get a DVT if you:

are over 40
are immobile, for example, if you have had an operation (especially on a hip or knee) or are travelling for long distances - and so are not able to move your legs
have had a blood clot in a vein before
have a family history of blood clots in veins
have a condition causing your blood to clot more easily (this is called thrombophilia)
are very overweight (obese)
have cancer or have had cancer treatment
have heart disease or circulation problems
are a woman taking a contraception pill that contains oestrogen, or hormone replacement therapy (HRT)
are pregnant or have recently had a baby

Travel risks

There is evidence that long-haul flights (lasting over four hours) can increase your risk of developing DVT. The risk is mainly the result of sitting down for long periods of time, which can happen during any form of long-distance travel, whether by car, bus, train or air.

It's difficult to say whether the travelling itself directly causes DVT, or whether people who get DVT after travelling are at risk for other reasons. Generally, your risk of developing DVT when travelling is very small unless you have at least one of the other risk factors mentioned above (such as a history of DVT or cancer). If this is the case, you should talk to your GP before you travel on a flight of more than four hours.

Diagnosis of DVT

Your GP will ask about your symptoms and examine you. If he or she thinks that you might have a DVT, you may be referred to a specialist. You may have the following tests in hospital.

A blood test called a D-Dimer. This measures a substance which develops when a blood clot breaks down. If this is negative it's unlikely that you have a DVT.
A Doppler ultrasound. This is a test that uses sound waves to look at your blood as it flows through your blood vessels. It's the best test to detect blood clots above your knee.
A venogram. In this test, a special dye is injected into your vein, which shows up the vein on X-ray. This is the best way of showing clots below your knee.

Treatment of DVT

Medicines

Anticoagulant medicines are the standard treatment for DVT. They change chemicals in your blood to stop clots forming so easily. Anticoagulants include heparin and warfarin. Anticoagulants can stop new blood clots from forming and old ones from getting any bigger. They can't dissolve clots that you already have - your body will do that itself over time.

Thrombolytic medicines are medicines that work by dissolving blood clots; but they can cause bleeding and so are rarely used to treat DVT.

Compression stockings

These are also called graduated compression stockings. Your doctor may ask you to wear these to ease your pain and reduce swelling, and to prevent post-thrombotic syndrome. You may need to wear them for two years or more after having a DVT.

Prevention of DVT

Ask your GP for advice if you think you're at risk of developing a DVT.

There are a number of things you may be able to do to reduce your risk, such as stopping smoking if you smoke, or losing weight if you're overweight. Regular walking can help to improve the blood circulation in your legs and help to prevent another DVT from developing.

There is no good evidence that taking aspirin reduces your risk of developing DVT.

If you're having surgery

Surgery and some medical treatments can increase your risk of developing DVT. So, if you're going to hospital for an operation, you will usually have an assessment to check your risk of developing DVT before you have your operation. There are many things that can be done to keep your risk of developing DVT during surgery as low as possible. You may be given anticoagulant medicines before and after surgery, or be asked to wear compression stockings. You may also be given a mechanical pump to use on your feet and legs in the first few days after the operation. This is called an intermittent compression device. The pump automatically squeezes your feet and lower legs to help your blood circulate.

If you're travelling

Although it's unlikely that you will develop DVT when you're travelling, there are some steps you can take to reduce your chances of developing a blood clot. These include:

take short walks - if you're a passenger, walk up and down the aisle of the coach, train or plane
exercise the muscles of your lower legs, which act as a pump for the blood in your veins - regularly bend and straighten your toes, ankles and legs
wear loose-fitting clothes
keep hydrated by making sure you drink enough water
don't drink too much alcohol or too many drinks that contain caffeine, such as coffee
don't take sleeping tablets, as these will stop you keeping your legs active
wear compression stockings if you have other risk factors for DVT

If your GP has told you that you're at high risk for DVT (for example, if you have a previous history of DVT or a blood clotting disorder), you may need heparin injections as well for flights longer than four hours. Talk to your GP or haematologist for more information.

If you develop swelling or pain in your calf or thigh, or if you have breathing problems or chest pain after travelling, you should seek urgent medical attention.