Deep vein thrombosis (DVT) is a blood clot that develops within a major vein in the body.

“DVT in the lower leg or thigh is the most common, although the arms and pelvis can also be at risk,” says Jay Brewer, Professional Head of Clinical Wellbeing at Nuffield Health. 

“Clots can limit the flow of blood in the veins causing pain and swelling. If the clot dislodges there is a danger of it travelling to the lungs, blocking the blood supply there (pulmonary embolism) and causing breathing problems. Not all blood clots cause DVT as your body usually absorbs them gradually.”

If left untreated, about one in 10 people with a DVT will develop a pulmonary embolism. A pulmonary embolism causes:

• Breathlessness – which may come on gradually or suddenly
• Chest pain – which may become worse when you breathe in
• Sudden collapse

What are the symptoms of DVT?

In some cases, there may be no symptoms.

If symptoms do occur they can include:

• Pain, swelling and tenderness in one of your legs (usually your calf)
• A heavy ache in the affected area
• Warm skin in the area of the clot
• Red skin, particularly at the back of your leg below the knee

DVT usually (although not always) affects one leg. The pain may be worse when you bend your foot upward towards your knee.

What are the risks of DVT happening to me?

Each year, DVT affects around one person in every 1,000 in the UK. Deep vein thrombosis (DVT) sometimes occurs for no apparent reason. But factors that may contribute to a higher chance of DVT are:

Your age. Your risk increases over the age of 40.

Smoking.

You or a close relative have previously been affected by DVT

Taking the combined pill or HRT. Oestrogen causes the blood to clot a bit more easily than normal, so your risk of getting DVT is slightly increased.

Pregnancy. Your blood clots more easily during pregnancy. It’s the body’s way of preventing too much blood being lost during childbirth. DVT and pulmonary embolism affect about one in 100,000 women of childbearing age, so they’re still rare. But pregnant women are up to 10 times more likely to develop thrombosis than non-pregnant women of the same age. A clot can form at any stage of pregnancy and up to six weeks after the birth.

You’re overweight or obese.

Blood vessel damage. If the wall of a blood vessel is damaged through injury such as broken bones or severe muscle damage, it may become narrowed or blocked, which can cause a blood clot to form.

You have a medical condition that causes your blood to clot more easily than normal. These conditions include cancer (treatments such as chemotherapy and radiotherapy can increase this risk further), heart disease and lung disease, infectious conditions, such as hepatitis and inflammatory conditions, such as rheumatoid arthritis.

Your mobility is restricted, for example, after an operation, because of an illness or injury, or during a long journey. When you’re inactive your blood flow can slow down considerably and fluid tends to collect in the lower parts of your body, often in your lower legs. This is usually nothing to worry about because when you start to move, your blood flow increases and moves evenly around your body. Swollen ankles and legs are common on long flights and not due to DVT.

“The human body was designed for movement, not to stay still. Prolonged sitting – staying in one position for a long period of time – adds to the static load on our musculoskeletal system and prevents effective circulation of blood through your body,” says Jay Brewer.

So how do I reduce my risk my DVT when I’m travelling?

Move around. “The key thing to remember during long flights is to stay as mobile as possible and avoid sitting in a particularly cramped position for long hours during flights,” says Mr Obiekezie Agu, consultant vascular surgeon at the The Harley Street Clinic’s Vascular Centre.

“Venous blood flow is relatively slow and susceptible to thrombosis following prolonged inactivity. Leg veins are therefore reliant on activity and movement to help the blood flow correctly

“Stretch your legs regularly and I advise making sure that you walk around often. In-flight hypoxia and low humidity may also contribute to increased blood viscosity. Travellers in economy class accommodation, who have their big veins squeezed behind the knees for long periods of time where movement is restricted, are naturally at greater risk than those in more relaxed business and first class seats.”

Drink lots of water. The recommendation is at least one litre of water for every five hours flying. “Dehydration can increase the concentration and viscosity of the blood, which when coupled with slow flow makes DVT more likely,” says Mr Agu. It’s best to steer clear of alcohol and sleeping pills. 

Get some compression stockings. Wearing elastic compression stockings during flights of four hours or more can significantly reduce your risk of DVT, as well as leg swelling (oedema).

The below-knee stockings apply gentle pressure to the ankle to improve circulation. They come in a variety of sizes and there are also different levels of compression.  

You can buy them from pharmacies and airport shops. It’s a good idea to take advice on the right size from a pharmacist.

“There is some benefit to using well-fitting flight compression stockings,” says Mr Agu.“They have been proven to prevent DVT for people at higher risk and those who are in immobilised positions for long periods of time.”

Wear loose comfortable clothing. Avoid socks, tights and skinny fit jeans that are too restrictive.  

Don’t sit with your legs crossed.  And do seated leg and ankle exercises to keep the blood moving. Circle each foot round, keeping the whole leg as still as possible, rotating from the ankle joint. Do 10 rotations anti-clockwise and clockwise with each foot. Push toes and ball of foot into the floor, hold for a count of five, then release. Now push your heel into the floor for a count of five, then release. 

Remember, DVT is relatively rare, but it’s still best to be prepared.