Diseases & Conditions
Deep vein thrombosis
Air travellers are at increased risk of DVT
Deep vein thrombosis is the formation of a blood clot in one of the deep veins of the body, usually in the leg. It is comparatively rare, affecting around one or two people in every thousand, mainly older people.
What is deep vein thrombosis?
Deep vein thrombosis, commonly referred to as DVT, is a disease of the circulation. It occurs most often in people who have not been able to exercise normally.
Blood passing through the deepest veins in the calf or thigh flows relatively slowly: when a DVT occurs it moves so slowly that it forms a solid clot which becomes wedged in the vein.
What are the symptoms?
Quite often there are no symptoms at all. Where they do exist there may be pain or tenderness in the leg and raised skin temperature around the area. Sudden swelling in one leg may be the first sign.
Occasionally some of the surface veins are more visible through the skin. There may also be pain on flexing the foot upwards.
How can a DVT be detected?
DVTs are most commonly detected nowadays by use of ultrasound - scientists say they can now use this method to detect even the smallest of clots.
Ultrasonographic testing identifies even the smallest of clots
Blood tests can also give a good indication that there is a thrombosis. One test which measures the levels of a by-product of clotting material called D-dimer is commonly used. If the doctor suspects a DVT he will usually request an urgent ultrasound and order blood tests.
How dangerous is it?
DVTs themselves are not life-threatening but they are associated with complications which can be fatal.
The most common serious complication is a pulmonary embolism which occurs in between one in three and one in four cases of DVT. A piece of the clot lodged in the leg vein breaks off and travels through the body to the lung, where it becomes lodged again causing severe breathing difficulties.
Untreated, up to one in ten people who suffer a pulmonary embolism die as a result.
More rarely, a part of the clot may also lodge in other organs including the brain, where it leads to a stroke.
One less serious complication is post-thrombotic syndrome, which affects many people after a DVT, due to damage to the valves along the length of the vein. It can cause pain and swelling and ulceration of the skin around the area.
How is DVT treated?
Around two thirds of people with a DVT need to be cared for in hospital in the initial stages. The aim is to dissolve the clot and, in the longer term, prevent other clots from forming.
The main treatment for DVT - or similar problems with clotting of the blood - is medicines which will thin the blood and allow it to flow more easily.
On diagnosis of a DVT, this usually initially involves giving high doses of the drug heparin by injection.
Too much bed rest is discouraged
Patients are also prescribed a similar drug, warfarin, in tablet form, which they may stay on for several months. When taking these blood thinning drugs patients usually have regular blood tests to make sure they are getting the right dose and are not at risk of a haemorrhage.
Painkillers and heat applied to the area may also be advised for relief of symptoms of a DVT.
Patients will be encouraged to move around as much as they can. Compression stockings are often worn to cover the length of the whole leg to give support to the veins and reduce swelling.
Are there any risk factors?
DVTs are rare in young people, usually occurring in people aged over 40.
There are a number of related conditions which increase the likelihood of developing a DVT
family history of DVT
paralyisis or immobility.
A DVT can happen after major surgery or a broken leg because of being unable to move the leg and encourage blood flow through it. This happens now than in the past, because gentle exercise is encouraged at the first opportunity.
Women taking the pill are three or four times more likely to suffer a DVT than those who don't and there is also an increased risk for women on hormone replacement therapy.
Women who are pregnant or who have recently given birth are also at increased risk of developing a DVT.
One group in whom DVTs are becoming more common are travellers. A French study has shown that journeys more than five hours long by car, plane or train increase the risk of DVT fourfold.
There is particular risk with air travel because of the combination of inactivity and dehydration, which makes the blood more sticky.
A recent study in The Lancet showed that as many as one in ten passengers could suffer DVT unless they wore the special compression stockings.
Can DVT be prevented?
People who have already had a DVT are more at risk of going on to develop another one.
Taking drug thinning drugs such as aspirin is one way to cut the risk of developing a clot. Taking a low dose of aspirin before a long flight, for example, may reduce risk as does walking around in the cabin.
Foot exercises while sitting down - rotating the ankles and wiggling the toes - prevents the blood pooling in the feet and then struggling to climb up through the veins.
Wearing compression stockings may also be advised for those at risk of developing a DVT.
Special foot cushions have been developed so passengers can exercise while sitting at their seats.
Keeping mobile is vital. Immediately after an operation, people are encouraged to get out of bed as early as possible, because of the chance that lying still may lead to a DVT.