Deep vein thrombosis

This factsheet is for people who have a deep vein thrombosis (DVT) or for people who wish to learn more about DVT.

A deep vein thrombosis (DVT) is a blood clot (thrombus) that develops in a deep vein, usually in the lower leg. Deep vein thrombosis can cause pain in the leg and can potentially lead to complications.¹

Where do DVTs happen?

A DVT usually develops in a deep vein in the leg but it can occur elsewhere, such as the arm. Deep veins pass through the centre of the leg and are surrounded by the muscles.

A DVT is different to blood clots that form in a separate set of veins (called superficial veins) that lie under the skin. These clots are called superficial thrombophlebitis and are much less serious.²

How is a DVT different to normal blood clotting?

When blood clots outside a blood vessel, this is a normal process which protects the body against losing blood. If the blood clots inside a blood vessel however (as with DVT), this can be dangerous.

Symptoms of DVT

In most cases of DVT, the clots are small and do not cause any symptoms. The body is able to gradually break down the clot and there are no long-term effects.³

Larger clots may partially or totally block the blood flow in the vein and cause symptoms such as:

swelling of the calf - this is usually different from the mild ankle swelling that many people get during long haul flights for example^1,3
pain in the calf³
calf pain that is noticeable, or worse when standing or walking³

These are not always a sign of a DVT, but if you experience them, you should seek medical advice.

Complications

It is uncommon for DVT to cause any further problems but potential complications include the following.

Pulmonary embolism (PE) happens when a piece of the blood clot breaks off and travels in the bloodstream to become lodged in the lungs and block blood flow. This can happen hours or even days after the formation of a clot in the calf veins. It may cause chest pain and shortness of breath. You should seek emergency medical treatment as a pulmonary embolism can be fatal in severe cases.^1,3
Post thrombotic syndrome happens if a DVT damages the valves in the vein, so that instead of flowing upwards, the blood pools in the lower leg. This can result in pain, swelling and ulcers on the leg.⁴

Illustration showing deep vein thrombosis in the leg

Causes of DVT

A DVT can be caused by a damaged vein or if the flow of blood slows down or stops. There are certain risk factors that make a DVT more likely to occur. These include:

age - as people over 40 are at greater risk of DVT^1,3,5
a past history of DVT^1,3,5
a family history of DVT^1,3,5
an inherited condition that makes the blood more likely to clot than usual^1,3,5
immobility^1,5
obesity^3,5
recent surgery or an injury, especially to the hips or knees^1,3,5
pregnancy^1,3,5
having recently had a baby^1,5
having cancer and its treatments^1,3,5
taking a contraceptive pill that contains oestrogen - but most modern pills contain a low-dose, which increases the risk by an amount that is acceptable for most women^1,3,5
hormone replacement therapy (HRT) - but for many women, the other benefits outweigh the increase in risk of DVT^1,3,5
treatment for other circulation or heart problems^1,5

Is air travel a risk?

There is evidence that long haul flights (flight lasting four hours or more) may increase the risk of developing DVT.¹ The risk is a result of prolonged immobility, which can happen during any form of long distance travel, whether by car, bus, train or air.³

It is difficult to say from results of studies:

whether the actual flight directly caused the DVT
whether these people were at risk of DVT for other reasons^1,5

Generally the risk of developing DVT when travelling is very small unless one or more other risk factors are present. If this is the case, you should seek advice from your GP before travelling on a flight of more than three hours.³ You should also seek advice if you have recently had a hip or knee replacement operation as ideally you should postpone long haul travel for three months after surgery.¹

Diagnosis

Your GP will ask you about your medical history and examine you. Your GP may refer you to a specialist for the following tests.

An ultrasound scan looks for blockages of blood flow in blood vessels.^2,4
A Doppler ultrasound shows how fast the blood is flowing.²
A venography shows the flow of blood. Special dye that shows up in X-rays is injected into the veins and then an X-ray is taken.^2,4

Treatment

Treatment aims to prevent:

the clot becoming larger
the blood clot breaking loose and travelling to the lungs
new clots from forming
post-thrombotic syndrome

Drug treatments

Anticoagulant medicines are the most common treatment. These alter certain chemicals in the blood to stop clots forming so easily. Anticoagulants include heparin which may be followed later by warfarin.⁶ Anticoagulants can stop new blood clots from forming and old ones growing in size. They can't dissolve existing clots. The body does this itself over time.

There have been concerns that cranberry juice can interfere with the way the anticoagulant, warfarin, works. The Committee on Safety of Medicines advises that you should not consume any cranberry products whilst taking warfarin.^6,7

In addition, you should not do any activities that could increase your risk of injury whilst taking anticoagulants. This is because one of the main ways a wound heals is through clotting, and anticoagulants interfere with this process.

Thrombolytics are used less commonly. These medicines are used to dissolve blood clots. They carry a high risk of bleeding, so are only used in severe cases.⁶

Compression stockings (also called graduated compression stockings) are sometimes recommended to relieve pain and swelling, and to prevent post thrombotic syndrome.⁸ These may need to be worn for two years or more after having a DVT.^4,5,8

Prevention

If you feel you are at high risk of developing a DVT you should seek medical advice.

You may also want to consider any measures you can take to reduce the risk. This could include keeping mobile, if possible, by exercising your legs regularly - for example take a brisk 30-minute walk every day.⁹

Around surgery

Surgery and some medical treatments can increase the risk of having a DVT. So, hospitals often do a pre-operative risk assessment for DVT, which takes into account your personal risk factors and the type of surgery you are having.

Various measures can then be used to keep the risk as low as possible. These include anticoagulant medicines, compression stockings, and intermittent calf compression devices. This is a mechanical pump that automatically squeezes the feet and lower legs. This helps the circulation of blood from the legs in the first few days after surgery.

Travelling

Although the added risk of developing a DVT caused by long haul travelling appears to be low, it can be reduced even further by taking some preventive measures. Wherever possible, you should:

exercise your legs at least every 2-3 hours - try to take regular breaks from driving. Or if you're a passenger, walk up and down the aisle of a coach, train or plane^1,3
exercise the muscles of your lower legs (which act as a pump for the blood in the veins) while sitting - pull your toes towards your knees then relax, or press the balls of your feet down while raising your heel^1,3
wear loose-fitting clothing^1,3
keep hydrated by drinking water rather than alcohol and caffeinated drinks¹
wear graduated compression stockings - this is particularly important for travellers who have other risk factors for DVT¹

If you develop swelling or pain in your leg, or have breathing problems after travelling, you should seek medical advice urgently.

Further information

Search for "deep vein thrombosis" on healthinsite.gov.au

References

Advice on travel-related DVT. Department of Health.
www.dh.gov.uk
accessed 17 November 2005
Deep vein thrombosis. NHS Direct Health Encyclopaedia.
www.nhsdirect.nhs.uk
accessed 21 November 2005.
International travel and health. World Health Organisation. 2005.
www.who.int
Simon C, Everitt H, Birtwistle J, Stevenson B. Oxford Handbook of General Practice. Oxford: Oxford University Press, 2002.
PRODIGY Guidance - Deep vein thrombosis. UK Department of Health. PRODIGY.
www.prodigy.nhs.uk
accessed 18 November 2005
BNF British National Formulary 50, September 2005.
Cranberry. Committee on Safety of Medicines of the MHRA.
www.mhra.gov.uk
19 August 2005.
Procedures for the outpatient management of patients with deep vein thrombosis. Haemostasis and Thrombosis Task Force of the British Committee for Standards in Haematology. October 2003.
www.bcshguidelines.com
Deep vein thrombosis (DVT). UK Department of Health. PRODIGY.
www.prodigy.nhs.uk
accessed 18 November 2005.

The information on this factsheet is intended to be a guide only and is not intended to be nor should be relied on as a substitute for professional medical advice. It is also not intended to be for medical diagnosis or treatment. BUPA Australia makes no warranties or representations regarding the quality, accuracy or completeness of the information. BUPA Australia is not liable to readers of the information for any loss or damage suffered arising out of the use of or reliance on the information, except that which can be excluded by law.