What is Deep Vein thrombosis?

A deep vein thrombosis (DVT) occurs when a blood clot forms in a vein. A DVT usually develops in the calf, but it sometimes also occurs in the thigh, and occasionally in other deep veins in your body.

Some of the common symptoms of a DVT are:

Some people may only realise they have a DVT when a pulmonary embolism develops as a result of the blood clot in the leg. pulmonary embolism is a very serious condition. See pulmonary embolism.

What causes a DVT?


Journeys, by any means of transport, where you sit still for long periods of time without being able to stretch your legs or move about. A medical condition or injury that restricts normal movement or activity.

Surgery or illness

Undergoing surgery may mean lying still for long periods of time. Staying in hospital as a medical patient may also involve long periods of imobility. Having some treatments such as chemotherapy, which may damage veins, can also increase your risk.

Genetic conditions

Some people have genetic conditions, such as Factor Five Leiden, which will increase their risk of a deep vein thrombosis.

Previous DVT

If you have already had a DVT then there may be some vein damage and you will be at a higher risk.

Contraceptive pill and hormone replacement therapy (HRT)

Both contraceptive pills and HRT therapy normally contain the hormone oestrogen. For some people, this can make their blood more likely to clot easily.


Approximately 1 in 1000 pregnant women will have a DVT.

Other reasonsIllustration: inside a vein

There has recently been some speculation that sitting at your desk for long periods of time may also be an increased risk for DVT.

It should also be noted that some people will have a DVT for no apparent reason.

Diagnosing a DVT

It can be difficult to diagnose a DVT as there may be many causes for a swollen and painful leg. However there are tests that can detect clots. The following three tests are often used. Treatment

It is essential to treat a DVT as quickly as possible to prevent the clot getting bigger or pieces of it breaking off and travelling to the lungs causing a pulmonary embolism.

Anticoagulation therapy

Heparin and warfarin are the two anticoagulants that are normally used to treat DVT. Anticoagulant therapy is often referred to as "thinning the blood". However it does not thin the blood but lengthens the time it takes for your blood to clot. This prevents clots for forming so easily. See the page Anticoagulation therapy.

Compression stockings

Wearing compression stockings may help to prevent further damage. They can also help to reduce pain and can also help stop post-thrombotic syndrome occurring. Post-thrombotic syndrome is damage to the tissues of your calf. It can cause pain and a rash. Leg ulcers may also occur.

Compression stockings need to fit properly and you will need to be measured by your health care professional (HCP). They should be worn every day. Your HCP will tell you how long you will need to wear them for.

Helping you to avoid a DVT

IMPORTANT: The following suggestions apply for any long journey, such as coach, train or car, and also when sitting for any lengthy period.


Anticoagulants. NMIHI. Accessed at http://drugs.nmihi.com/anticoagulants.htm on June 11, 2018.

DVT. MedlinePlus. Accessed at https://medlineplus.gov/ on June 11, 2018.

DVT: Treatment. NHS. Accessed at https://www.nhs.uk/ on June 11, 2018.