Deep vein thrombosis (DVT)

Published by Bupa's Health Information Team, July 2011.

This factsheet is for people who have deep vein thrombosis (DVT), or who would like information about it including the symptoms, causes and treatments.

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

Animation - how DVT 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). It can also develop in the deep veins in your thigh and, more rarely, in other deep veins, such as the ones in your arm or pelvis.

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

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, although they can occasionally spread to deep veins.

Symptoms of DVT

Many blood clots 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 in your affected leg or arm such as:

• swelling 
• pain and tenderness - 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 
• a mild fever

Although these symptoms may not be caused by DVT, if you have these symptoms you should visit your GP for advice.

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 breaks off and travels through your bloodstream to your lungs, where it blocks one of the blood vessels. This is serious and can be fatal. See Related topics for further information.

Post thrombotic syndrome

This happens if the damage caused by a DVT permanently reduces the ability of your veins to efficiently return blood from your lower leg and leads to pooling of fluid. This can eventually lead to long-term pain and swelling. In severe cases these may lead to ulcers on your leg.

Limb ischaemia

This is a rare complication that only happens with a large DVT. The blood clot can cause the pressure in your vein to become high. This can block the flow of blood through your arteries, so less oxygen is carried to your 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 60
• smoke 
• are immobile, for example, if you have had an operation (especially on your hip or knee) or are bed bound
• are travelling for long distances and aren’t able to move your legs 
• have had a blood clot in a vein before 
• have a family history of blood clots in veins 
• have an inherited condition causing your blood to clot more easily (this is called thrombophilia) 
• are very overweight (obese) 
• have cancer, heart disease, inflammatory bowel disease, kidney disease or other long-term illnesses 
• have a condition where your blood is at a higher risk of clotting than normal (antiphospholipid syndrome)
• 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.

Generally, your risk of developing DVT when travelling is small unless you have at least one of the risk factors mentioned above. 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 in hospital or clinic for full assessment. You may then have the following tests.

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

There are things you can 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 circulation in your legs and help to prevent another DVT from developing. If you have had a DVT, you can usually start walking once you get home from the hospital, unless your doctor has told you otherwise.

There isn't enough evidence to show 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

If you have recently been treated for DVT, you should wait two weeks before travelling on longer journeys.

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 on journeys of over four hours. For example, you should:

• take short walks – if you're a passenger, walk up and down the aisle of the 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 
• not drink too much alcohol or too many drinks that contain caffeine, such as coffee 
• not 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 previously had DVT or you have a blood clotting disorder), you may also need heparin injections for flights longer than six hours. Talk to your GP or haematologist for more information.

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

For answers to frequently asked questions on this topic, see FAQs.

For sources and links to further information, see Resources.