Deep vein thrombosis (DVT) is a blood clot that develops within a deep vein in the body, usually in the leg.
Blood clots that develop in a vein are also known as venous thrombosis.
DVT usually occurs in a deep leg vein, a larger vein that runs through the muscles of the calf and the thigh.
It can cause pain and swelling in the leg and may lead to complications such as pulmonary embolism. This is a serious condition that occurs when a piece of blood clot breaks off into the bloodstream and blocks one of the blood vessels in the lungs (see below).
DVT and pulmonary embolism together are known as venous thromboembolism (VTE).
Deep vein thrombosis signs and symptoms can include:
- Swelling in the affected leg. Rarely, there’s swelling in both legs.
- Pain in your leg. The pain often starts in your calf and can feel like cramping or soreness.
- Red or discoloured skin on the leg.
- A feeling of warmth in the affected leg.
- Deep vein thrombosis can occur without noticeable symptoms.
When to see a doctor
If you develop signs or symptoms of deep vein thrombosis, contact your doctor.
If you develop signs or symptoms of a pulmonary embolism — a life-threatening complication of deep vein thrombosis — seek immediate medical attention.
The warning signs and symptoms of a pulmonary embolism include:
- Sudden shortness of breath
- Chest pain or discomfort that worsens when you take a deep breath or when you cough
- Feeling lightheaded or dizzy, or fainting
- Rapid pulse
- Coughing up blood
Many factors can increase your risk of developing deep vein thrombosis (DVT). The more you have, the greater your risk of DVT. Risk factors include:
- Inheriting a blood-clotting disorder. Some people inherit a disorder that makes their blood clot more easily. This condition on its own might not cause blood clots unless combined with one or more other risk factors.
- Prolonged bed rest, such as during a long hospital stay, or paralysis. When your legs remain still for long periods, your calf muscles don’t contract to help blood circulate, which can increase the risk of blood clots.
- Injury or surgery. Injury to your veins or surgery can increase the risk of blood clots.
- Pregnancy. Pregnancy increases the pressure in the veins in your pelvis and legs. Women with an inherited clotting disorder are especially at risk. The risk of blood clots from pregnancy can continue for up to six weeks after you have your baby.
- Birth control pills (oral contraceptives) or hormone replacement therapy. Both can increase your blood’s ability to clot.
- Being overweight or obese. Being overweight increases the pressure in the veins in your pelvis and legs.
- Smoking. Smoking affects blood clotting and circulation, which can increase your risk of DVT.
- Cancer. Some forms of cancer increase substances in your blood that cause your blood to clot. Some forms of cancer treatment also increase the risk of blood clots.
- Heart failure. This increases your risk of DVT and pulmonary embolism. Because people with heart failure have limited heart and lung function, the symptoms caused by even a small pulmonary embolism are more noticeable.
- Inflammatory bowel disease. Bowel diseases, such as Crohn’s disease or ulcerative colitis, increase the risk of DVT.
- A personal or family history of deep vein thrombosis or pulmonary embolism. If you or someone in your family has had one or both of these, you might be at greater risk of developing a DVT.
- Age. Being older than 60 increases your risk of DVT, though it can occur at any age.
- Sitting for long periods of time, such as when driving or flying. When your legs remain still for hours, your calf muscles don’t contract, which normally helps blood circulate. Blood clots can form in the calves of your legs if your calf muscles don’t move for long periods.
Practical Steps to Keep DVT Risk Low
- Ask your doctor about need for “blood thinners” or compression stockings to prevent clots, whenever you go to the hospital
- Lose weight, if you are overweight
- Stay active
- Exercise regularly; walking is fine
- Avoid long periods of staying still
- Get up and move around at least every hour whenever you travel on a plane, train, or bus, particularly if the trip is longer than 4 hours
- Do heel toe exercises or circle your feet if you cannot move around
- Stop at least every two hours when you drive, and get out and move around
- Drink a lot of water and wear loose fitted clothing when you travel
- Talk to your doctor about your risk of clotting whenever you take hormones, whether for birth control or replacement therapy, or during and right after any pregnancy
- Follow any self-care measures to keep heart failure, diabetes, or any other health issues as stable as possible
“When you’re inactive your blood 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.
However, if you’re unable to move for a long period of time – such as after an operation, because of an illness or injury, or during a long journey – your blood flow can slow down considerably. A slow blood flow increases the chances of a blood clot forming.”
- In hospital
“If you have to go into hospital, your risk of getting a blood clot increases. This is because DVT is more likely to occur when you’re unwell or inactive, or less active than usual.
As a patient, your risk of developing DVT depends on the type of treatment you’re having. You may be at increased risk of DVT if any of the following apply:
you’re having an operation that takes longer than 90 minutes, or 60 minutes if the operation is on your leg, hip or abdomen
you’re having an operation for an inflammatory or abdominal condition, such as appendicitis
you’re confined to a bed, unable to walk, or spending a large part of the day in a bed or chair for at least 3 days
You may also be at increased risk of DVT if you’re much less active than usual because of an operation or serious injury and have other DVT risk factors, such as a family history of the condition.
When you’re admitted to hospital you should be assessed for your risk of developing a blood clot, whatever type of treatment you’re having, and, if necessary, given preventative treatment.”
- Blood vessel damage
“If the wall of a blood vessel is damaged, it may become narrowed or blocked, which can cause a blood clot to form.
Blood vessels can be damaged by injuries such as broken bones or severe muscle damage. Sometimes, blood vessel damage that occurs during surgery can cause a blood clot, particularly in operations on the lower half of your body.
Conditions such as vasculitis (inflammation of the blood vessels), varicose veins and some forms of medication, such as chemotherapy, can also damage blood vessels.”
- Medical and genetic conditions
“Your risk of getting DVT is increased if you have a condition that causes your blood to clot more easily than normal. These conditions include:
- cancer – cancer treatments such as chemotherapy and radiotherapy can increase this risk further
- heart disease and lung disease
- infectious conditions, such as hepatitis
- inflammatory conditions, such as rheumatoid arthritis
- thrombophilia – a genetic condition where your blood has an increased tendency to clot
- antiphospholipid syndrome – an immune system disorder that causes an increased risk of blood clots”
“During pregnancy, blood clots more easily. It’s the body’s way of preventing too much blood being lost during childbirth.
Venous thromboembolism (VTE) – DVT and pulmonary embolism – affects about one in 100,000 women of childbearing age.
DVTs are also rare in pregnancy, although 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.
Having thrombophilia (a condition where the blood has an increased tendency to clot), or having a parent, or brother or sister, who’s had a thrombosis, increase your risk of developing a DVT during pregnancy.”
Other risk factors during pregnancy include:
- being over 35 years old
- being obese (with a BMI of 30 or more)
- expecting 2 or more babies
- having recently had a caesarean section
- being immobile for long periods of time
- smoking (find out how to stop smoking)
- having severe varicose veins
“Low molecular weight heparin (LMWH) is usually used to treat pregnant women with DVT. LMWH is an anticoagulant, which means it prevents the blood clot getting bigger. It’s given by injection and doesn’t affect your developing baby.”
- Contraceptive pill and HRT
“The combined contraceptive pill and hormone replacement therapy (HRT) both contain the female hormone oestrogen. Oestrogen causes the blood to clot a bit more easily than normal, so your risk of getting DVT is slightly increased. There’s no increased risk from the progestogen-only contraceptive pill.”
Your risk of getting DVT is also increased if you or a close relative have previously had DVT and:
you’re overweight or obese
you’re over 60 – particularly if you have a condition that restricts your mobility