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What is DVT?

DVT is a serious condition where blood clots develop in the deep veins of the legs. It must be distinguished from blood clots in superficial varicose veins in the legs, called phlebitis, which is much less serious.

One in every hundred people who develop DVT dies. The cause of death is usually a blood clot, travelling from the legs to the lungs. This is called pulmonary embolus or PE. When PE is severe it causes the lungs to collapse and heart failure.  DVT combined with PE or other blood clots is often referred to as Venous Thrombo-Embolism or VTE.

Treatment of DVT and PE is with blood-thinning drugs or anticoagulants, including warfarin and heparin. Aspirin in low doses also acts as a blood thinning drug and is used to prevent clotting conditions in the arteries like coronary thrombosis. Its benefit in preventing DVT is debatable.

Who is at risk from DVT

Every year DVT occurs in about 1-3 in 1000 people in the general population, ranging from less than 1 in 3000 in people under the age of 40 up to 1 in a few hundred in those over 80.

The risk of DVT and PE is greater in people:

DVT is also more common in women who:

These groups make up 90 to 95% of all those who get DVT and/or PE.

The risk of DVT from air travel

There is evidence that long-haul flights, especially when passengers have little or no exercise, may increase the risk of developing DVT. Information on the proportion of people who develop DVT related to air travel  has been limited until recently; new research carried out by a consortium of medical research scientists under the auspices of the World Health Organisation has found one case of DVT for every 6000 journeys that lasted 4 hours or more. Nevertheless, it is difficult to decide whether the flight itself caused the DVT/PE or whether these people were at risk for other reasons. This is because

While it is difficult to be certain what the exact causes of travel-related DVT are, experts agree that lack of exercise or immobility are major underlying risks. They have also identified that people at increased risk of DVT/PE in general are those more likely to develop travel-related DVT/PE.

What are the signs of DVT?

You may get swelling, pain, tenderness and redness especially at the back of the leg below the knee. This is different from the mild ankle swelling that many people get during long haul flights and DVT usually though not always affects only one leg. These complaints may develop during the journey but more commonly hours or even days and up to 4 weeks later. The pain may be made worse by bending the foot upward towards the knee. In some cases there may be no signs or symptoms of DVT at all in the legs and problems only become obvious when a pulmonary embolus or PE develops from the clots in the legs. Fortunately PE is rare. PE can cause breathlessness, chest pain and in severe cases, collapse and death. Both DVT and PE, whatever the cause, are serious conditions and need urgent investigation and treatment.

How to reduce the possible risks

Simple in-flight exercises and getting up and walking around regularly are advised.

Before the trip

Consult your doctor if you have:

Experts advise that people who have had hip or knee replacements should postpone long haul flights for three months after surgery. If you have had this kind of surgery, talk to your family doctor, travel clinic staff or a member of the surgical team.

You may need advice on in-seat exercises, especially leg exercises to keep the circulation active and reduce the risk of developing a DVT. Some information is provided below. More information is available in literature provided by travel agents, and in the in-flight leaflets magazines and videos now produced by many airlines.

You may also need to discuss treatment with blood-thinning drugs or the use of graduated compression stockings if you are in a high-risk group. Graduated compression stockings are widely available from pharmacies and pharmacists can provide advice on use and fitting.  While there is evidence that graduated compression stockings may be useful there is no evidence that aspirin is effective in preventing travel-related DVT or PE. Because aspirin can have serious side effects like bruising, bleeding from the gut and allergies you should consult your doctor before deciding to take this drug. People taking aspirin already should not increase the dose.

Women taking the 'pill' or on hormone replacement therapy (HRT) should do the exercises described in this advice to help reduce the risk. They should also discuss the use of graduated compression stockings with their community pharmacist. Women who are pregnant, or have recently had a baby should seek advice from the antenatal team or the health visitor.

Make sure you have good medical insurance for your trip. If you are travelling within the European Economic Area or Switzerland, you may be eligible for cover provided by the European Health Insurance Card (EHIC).  The EHIC entitles those eligible for cover to reduced cost healthcare where treatment becomes necessary during a temporary visit to other counties of the European Economic Area or Switzerland.  The card is only valid for treatment offered under the state healthcare schemes operating in these countries: it gives you access to treatment under the same terms as people that live in the country you are visiting.  However, the EHIC is not a substitute for travel insurance.  It may not cover all health costs and never covers repatriation costs.  Further information, including a full list of countries covered along with details of their 'health systems' can be found in the booklet 'Health Advice for Travellers' available from the Post Office and on line using the link below.

During the trip

After the trip

For the vast majority of air passengers there will be no problems upon disembarkation. However symptoms of DVT can appear after arrival. If you develop swollen painful legs, especially where one is more affected than the other, or if you have breathing difficulties, see a local doctor urgently or go the the nearest A&E department.

Research into travel-related DVT

More research is needed to explore effective methods of prevention of DVT.The Aviation Health Working Group (AHWG) is an interdepartmental organisation, chaired by the Department for Transport, with representatives from the Civil Aviation Authority, Health and Safety Executive and the Department of Health.  It meets every two months to discuss issues relevant to aviation health and oversees research and advises the air industry. The group also helps to ensure that further research ties in with that recently carried out under the auspices of the World Health Organisation.