Health A to Z
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).
In some cases, there may be no symptoms of DVT. If symptoms do occur they can include:
DVT usually (although not always) affects one leg. The pain may be worse when you bend your foot upward towards your knee.
If left untreated, about 1 in 10 people with a DVT will develop a pulmonary embolism. A pulmonary embolism is a very serious condition that causes:
Both DVT and pulmonary embolism require urgent investigation and treatment.
Seek immediate medical attention if you have pain, swelling and tenderness in your leg, and you develop breathlessness and chest pain.
Read more about the complications of DVT.
Each year, DVT affects around 1 person in every 1,000 in the UK.
Anyone can develop DVT, but it becomes more common over the age of 40. As well as age, there are also a number of other risk factors, including:
The combined contraceptive pill and hormone replacement therapy (HRT) both contain the female hormone oestrogen, which causes the blood to clot more easily. If you're taking either of these, your risk of developing DVT is slightly increased.
Read more about the causes of DVT.
See your GP as soon as possible if you think you may have DVT – for example, if you have pain, swelling and a heavy ache in your leg. They'll ask you about your symptoms and medical history.
It can be difficult to diagnose DVT from symptoms alone, so your GP may advise that you have a specialised blood test called a D-dimer test.
This test detects pieces of blood clot that have been broken down and are loose in your bloodstream. The larger the number of fragments found, the more likely it is that you have a blood clot in your vein.
However, the D-dimer test isn't always reliable because blood clot fragments can increase after an operation, injury or during pregnancy. Additional tests, such as an ultrasound scan, will need to be carried out to confirm DVT.
An ultrasound scan can be used to detect clots in your veins. A special type of ultrasound called a Doppler ultrasound can also be used to find out how fast the blood is flowing through a blood vessel. This helps doctors identify when blood flow is slowed or blocked, which could be caused by a blood clot.
A venogram may be used if the results of a D-dimer test and ultrasound scan can't confirm a diagnosis of DVT.
During a venogram, a liquid called a contrast dye is injected into a vein in your foot. The dye travels up the leg and can be detected by X-ray, which will highlight a gap in the blood vessel where a clot is stopping the flow of blood.
Treatment for DVT usually involves taking anticoagulant medicines, which reduce the blood's ability to clot and stop existing clots getting bigger.
Heparin and warfarin are two types of anticoagulant often used to treat DVT. Heparin is usually prescribed first because it works immediately to prevent further clotting. After initial treatment, you may also need to take warfarin to prevent another blood clot forming.
A number of anticoagulants, known as directly acting oral anticoagulants (DOACs), may also be used to treat conditions such as DVT. These medications include rivaroxaban and apixaban, and they've been shown to be as effective as heparin and warfarin with less serious side effects.
Read more about treating DVT.
If you need to go into hospital for surgery, a member of your care team will assess your risk of developing a blood clot while you're there.
If you're at risk of developing DVT, there are a number of things you can do to prevent a blood clot occurring, both before you go into hospital, such as temporarily stopping taking the combined contraceptive pill, and while you're in hospital, such as wearing compression stockings.
When you leave hospital, your care team may also make a number of recommendations to help prevent DVT returning or complications developing. These may include:
There's no evidence to suggest that taking aspirin reduces your risk of developing DVT.
See your GP before embarking on long-distance travel if you're at risk of getting DVT, or if you've had DVT in the past.
When taking a long-distance journey (six hours or more) by plane, train or car, you should take steps to avoid getting DVT, such as drinking plenty of water, performing simple leg exercises and taking regular, short walking breaks.
Read more about preventing DVT.
Deep vein thrombosis (DVT) sometimes occurs for no apparent reason.
However, the risk of developing DVT is increased in certain circumstances.
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.
If you have to go into hospital for an operation or procedure, 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 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'll be assessed for your risk of developing a blood clot and, if necessary, given preventative treatment.
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.
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:
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:
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.
Read more about DVT in pregnancy.
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:
If you have deep vein thrombosis (DVT), you'll need to take a medicine called an anticoagulant.
Although they're often referred to as "blood-thinning" medicines, anticoagulants don't actually thin the blood. They alter proteins within it, which prevents clots forming so easily.
Heparin and warfarin are two types of anticoagulants that are used to treat DVT. Heparin is usually prescribed first because it works immediately to prevent further clotting. After this initial treatment, you may also need to take warfarin to prevent another blood clot forming.
Heparin is available in two different forms:
Standard (unfractioned) heparin can be given as:
LMWH is usually given as a subcutaneous injection.
The dose of standard (unfractionated) heparin to treat a blood clot varies significantly from person to person, so the dosage must be carefully monitored and adjusted if necessary. You may need to stay in hospital for 5 to 10 days and have frequent blood tests to ensure you receive the right dose.
LMWH works differently from standard heparin. It contains small molecules, which means its effects are more reliable and you won't have to stay in hospital and be monitored.
Both standard heparin and LMWH can cause side effects, including:
In rare cases, heparin can also cause an extreme reaction that makes existing blood clots worse and causes new clots to develop. This reaction, and weakening of your bones, is less likely to occur when taking LMWH.
In most cases, you'll be given LMWH because it's easier to use and causes fewer side effects.
Warfarin is taken as a tablet. You may need to take it after initial treatment with heparin to prevent further blood clots occurring. Your doctor may recommend that you take warfarin for three to six months. In some cases, it may need to be taken for longer, even for life.
As with standard heparin, the effects of warfarin vary from person to person. You'll need to be closely monitored by having frequent blood tests to ensure you're taking the right dosage.
When you first start taking warfarin, you may need to have two to three blood tests a week until your regular dose is decided. After this, you should only need to have a blood test every four weeks at an anticoagulant outpatient clinic.
Warfarin can be affected by your diet, any other medicines you're taking and by how well your liver is working.
If you're taking warfarin you should:
Warfarin isn't recommended for pregnant women who are given heparin injections for the full length of treatment.
Rivaroxaban is a medication recommended by the National Institute for Health and Care Excellence (NICE) as a possible treatment for adults with DVT, or to help prevent recurrent DVT and pulmonary embolism.
Rivaroxaban comes in tablet form. It's a type of anticoagulant known as a directly acting oral anticoagulant (DOAC). It prevents blood clots forming by inhibiting a substance called factor Xa and restricting the formation of thrombin (an enzyme that helps blood clot).
Treatment usually lasts three months and involves taking rivaroxaban twice a day for the first 21 days and then once a day until the end of the course.
Read the NICE guidance about rivaroxaban for the treatment and prevention of recurrent deep vein thrombosis and pulmonary embolism.
NICE also recommends apixaban as a possible method of treatment and prevention for DVT and pulmonary embolism.
Like rivaroxaban, apixaban is a DOAC that's taken orally as a tablet, and prevents blood clots forming by hindering factor Xa and restricting the formation of thrombin.
Treatment usually lasts at least three months and involves taking apixaban twice a day.
Read the NICE guidance about apixaban for the treatment and secondary prevention of deep vein thrombosis and pulmonary embolism.
If you have had DVT, you should not be offered special stockings, called compression stockings, to stop you getting it again or to stop you from getting post-thrombotic syndrome. This is because it isn't clear if stockings help prevent these conditions.
Your healthcare team may still offer you stockings to treat your DVT or post-thrombotic syndrome symptoms, if they think it will help.
Your healthcare team will usually advise you to walk regularly once compression stockings have been prescribed. This can help prevent symptoms of DVT returning and may help to improve or prevent complications of DVT, such as post-thrombotic syndrome.
You might be advised to raise your leg whenever you're resting. This helps to relieve the pressure in the veins of the calf and stops blood and fluid pooling in the calf itself.
When raising your leg, make sure your foot is higher than your hip. This will help the returning blood flow from your calf. Putting a cushion underneath your leg while you're lying down should help raise your leg above the level of your hip.
You can also slightly raise the end of your bed to ensure that your foot and calf are slightly higher than your hip.
Read more about preventing DVT.
Inferior vena cava (IVC) filters are sometimes used as an alternative to anticoagulant medicines. This is usually because anticoagulant treatment needs to be stopped, isn't suitable or isn't working.
IVC filters are small mesh devices that can be placed in a vein. They trap large fragments of a blood clot and stop it travelling to the heart and lungs. They can be used to help prevent blood clots developing in the legs of people diagnosed with:
IVCs can be placed in the vein permanently, or newer types of filters can be placed temporarily and removed after the risk of a blood clot has decreased.
The procedure to insert an IVC filter is carried out using a local anaesthetic (where you're awake but the area is numb). A small cut is made in the skin and a catheter (a thin, flexible tube) is inserted into a vein in the neck or groin area. The catheter is guided using an ultrasound scan. The IVC filter is then inserted through the catheter and into the vein.
The two main complications of deep vein thrombosis (DVT) are pulmonary embolism and post-thrombotic syndrome.
A pulmonary embolism is the most serious complication of DVT. It happens when a piece of blood clot (DVT) breaks off and travels through your bloodstream to your lungs, where it blocks one of the blood vessels. In severe cases this can be fatal.
If the clot is small, it might not cause any symptoms. If it's medium-sized, it can cause chest pain and breathing difficulties. A large clot can cause the lungs to collapse, resulting in heart failure, which can be fatal.
About one in 10 people with an untreated DVT develops a severe pulmonary embolism.
If you've had a DVT, you may develop long-term symptoms in your calf known as post-thrombotic syndrome. This affects around 20-40% of people with a history of DVT.
If you have DVT, the blood clot in the vein of your calf can divert the flow of blood to other veins, causing an increase in pressure. This can affect the tissues of your calf and lead to symptoms, including:
When a DVT develops in your thigh vein, there's an increased risk of post-thrombotic syndrome occurring. It's also more likely to occur if you're overweight or if you've had more than one DVT in the same leg.
If you're admitted to hospital or planning to go into hospital for surgery, your risk of developing a blood clot while you're there will be assessed.
Surgery and some medical treatments can increase your risk of developing DVT – see causes of DVT for more information.
If you're thought to be at risk of developing DVT, your healthcare team can take a number of measures to prevent a blood clot forming.
If you're going into hospital to have an operation, and you're taking the combined contraceptive pill or hormone replacement therapy (HRT), you'll be advised to temporarily stop taking your medication four weeks before your operation.
There are a number of things your healthcare team can do to help reduce your risk of getting DVT while you're in hospital.
For example, they'll make sure you have enough to drink so you don't become dehydrated, and they'll also encourage you to move around as soon as you're able to.
Depending on your risk factors and individual circumstances, a number of different medications can be used to help prevent DVT. For example:
Compression stockings or compression devices are also commonly used to help keep the blood in your legs circulating.
Compression stockings are worn around your feet, lower legs and thighs, and fit tightly to encourage your blood to flow more quickly around your body.
Compression devices are inflatable and work in the same way as compression stockings, inflating at regular intervals to squeeze your legs and encourage blood flow.
Your healthcare team will usually advise you to walk regularly after you've been prescribed compression stockings. Keeping mobile can help prevent the symptoms of DVT returning and may help prevent or improve complications of DVT, such as post-thrombotic syndrome.
Read more about treating DVT.
You may need to continue to take anticoagulant medicine and wear compression stockings when you leave hospital.
Before you leave, your healthcare team should advise you about how to use your treatment, how long to continue using it for, and who to contact if you experience any problems.
You can reduce your risk of getting DVT by making changes to your lifestyle, such as:
See your GP before long-distance travel if you're at risk of getting a DVT, or if you've had a DVT in the past.
If you're planning a long-distance plane, train or car journey (journeys of six hours or more), make sure you:
Read more about preventing DVT when you travel.
If you're travelling abroad, it's very important to ensure you're prepared should you or a family member fall ill.
Make sure you have full travel insurance to cover the cost of any healthcare you may need while abroad. This is particularly important if you have a pre-existing medical condition, such as cancer or heart disease, which may increase your risk of developing DVT.
DVT can be a very serious condition, and it's important you receive medical assistance as soon as possible. Treating DVT promptly will help minimise the risk of complications.
Read more about travel health.
Journalist Mark Pownall from north London developed deep vein thrombosis (DVT) on a long-haul flight from New Orleans to London.
He'd been in the US for a medical conference in March 2004, reporting on topics including DVT. The night before his journey home, Mark had a few drinks.
The flight was hard work, with a six-hour transit in Washington DC because of delays. "Door to door, it was a 20-hour trip," said Mark.
"I arrived at Heathrow feeling like I'd slept quite badly. I felt a cramp in my left leg, and it got worse over the next few days."
It was only when Mark began limping because of the pain that he got medical attention at the insistence of his wife, Jill.
"My leg was hot and swollen," said Mark. His GP diagnosed DVT and he was sent to the Whittington Hospital in north London, where he received an ultrasound that found a blood clot stretching from his calf to his mid-thigh. "The clot had spread quite a bit."
Mark was kept in hospital and had to remain there for a few days. He received daily injections of the anti-clotting treatment heparin and was put on a course of warfarin tablets to prevent further blood clots.
"It's ironic that I got DVT after attending a conference about it," says Mark. "I should have known better and gone straight to my GP."
Doctors were puzzled by Mark's DVT. He didn't have any of the risk factors; he was male, a non-smoker, he was a healthy weight and had no family history of DVT. They said the long flight, dehydration and a lack of movement contributed to it.
After six months, Mark stopped taking warfarin because doctors thought he was unlikely to have another clot. But he did. In June 2007, Mark developed pain in the same leg, and the consequences could have been far worse.
"It was a dull muscular pain, which came and went," says Mark. But even then, despite having experienced DVT, Mark didn't realise what it was. "I think I was in denial," he says.
After a few days, he developed severe chest pains. He went to hospital, where a spiral CT scan found five blood clots in his lungs, known as a pulmonary embolism (PE). "Part of the clot in my leg had broken off and got into my pulmonary artery," says Mark. PE is a potentially fatal condition.
Mark was in hospital for four days, where he was treated with heparin and warfarin. "I was very lucky," says Mark. "I was healthy and that's why I’m still alive.
"With the first DVT I just thought I was unlucky, but with the second one it was the first time I'd come face to face with my own mortality.
"Doctors blamed the PE on the fact that I was sitting down for hours on end at my desk without moving, and not drinking enough water," he says.
Mark is now in a high-risk category and he'll probably need to continue taking warfarin for the rest of his life. When flying, he wears compression stockings to boost the circulation in his legs (flight socks have a similar effect).
"During the flight I make sure I drink water regularly, don't drink alcohol or coffee, and exercise," he says. "I try not to fall asleep either because that means I'm not moving."
Helen Cannings developed venous thromboembolism (VTE) at around 30 weeks of pregnancy. Her father also died of pulmonary embolism at the age of just 49.
"My dad died suddenly 10 years ago from a pulmonary embolism (PE). He was only 49 and it was a real shock for my whole family. Before he died, I didn't know much about VTE, apart from that you could get DVT from flying and should try to move your legs around on long flights.
"After dad died I had to have tests to check that I didn't have any genetic conditions that make your blood clot. I was given the all-clear, so didn't think I was at risk.
"I was about 29 weeks into my pregnancy when I woke up one morning and couldn't feel my left leg. It felt numb and dull. I thought it was cramp, so I got up and walked around, but it was hard to walk and the pain seemed to get worse. When I looked at my leg it was really swollen and an ashen grey colour.
"My partner, Tony, persuaded me to go to hospital to get it checked out. Luckily, it was a quiet Saturday morning, so I was admitted to the labour ward straight away.
"As the morning went on I could feel the pain in my leg getting worse. The doctor measured the size of my leg, felt the temperature, looked at the appearance of the skin and asked me a lot of questions about how I was feeling and my family history. It was confirmed that I had DVT, and I had to have an ultrasound scan to show the extent of the clot. It was just above the back of my knee and a few centimetres long.
"I was shocked and scared after my diagnosis. Because Dad had died from a pulmonary embolism, I was worried that the clot could move up to my lung. The whole thing brought a lot of emotions flooding back. Thankfully, I was reassured that my baby was ok. I was just worried about what could happen to me.
"I was put straight on to an anticoagulant medication. I couldn't take warfarin tablets because I was pregnant, so I had to have heparin. Heparin has to be taken as an injection, so I learned to do this myself before I left the hospital. I had to inject myself twice a day in the thigh. It was hard at first, but I soon got used to it. Taking the medication made me feel safer because I knew it would stop my blood clotting.
"Looking back, it was a stressful time. I was heavily pregnant and really worried about my health. I was told to rest and elevate my leg, but the pain didn't go away for about a month. I couldn't drive and could only really walk short distances, otherwise my leg would swell up. I was worried I'd never be able to move my leg normally again and worried about giving birth.
"My consultant and the team at the hospital took a while to decide how they were going to manage my labour. They decided I should have a natural birth, but would need to come off the heparin 12 hours before so I didn't lose too much blood. In the end, everything went well and my son Joseph was born healthy and happy.
"After giving birth, I was only discharged from hospital after a visit to the anticoagulant clinic to check how fast my blood was clotting. They found I was still at risk, so I was put on warfarin.
"I had to take the warfarin tablets for six months before having another review. I also had to wear compression stockings every day for two years. I've been told that if I ever have any chest pains, I should go straight to hospital because I'm at risk of pulmonary embolism.
"Although I knew there was a higher risk of blood clots in pregnancy, I didn't think I was high risk. I'm much more aware now and I think the fear of having another clot, and it being more serious, will always be at the back of my mind."
Battling through three different cancers meant that getting blood clots was the last thing on Jeremy Smith's mind.
"I got the first DVT after I was diagnosed with non-Hodgkin lymphoma. It was a traumatic time. I had a large tumour at the base of my spine and smaller tumours dotted around the lymph nodes of my abdomen. I was really quite ill, awaiting treatment and feeling very emotional. Even though I knew I had a family history of clots and strokes, and that non-Hodgkin lymphoma put me at increased risk, DVT was the last thing on my mind.
"My right leg became gradually swollen, but I thought it was probably just a reaction to the other things going on in my body. I thought it might be caused by the growing tumour in my spine pressing on the nerves of my leg.
"Eventually, I went to my spinal consultant to get it checked out. He did a pulse test on both my legs and found it was different in each one. He immediately thought I might have a clot. I was sent for an ultrasound scan that confirmed a large clot in a vein on the inside of my right leg.
"Having a DVT didn't seem like a big deal at the time because I had so many other things going on in my body and it was just another thing to deal with. As well as the other treatments I was having for cancer, which included chemotherapy and surgery, I had treatment for DVT. I had to wear compression stockings and take warfarin to protect me from getting further clots.
"I was on and off the warfarin because I had to have surgery to treat my cancer. You can't take warfarin if you're having surgery because it thins the blood and you could lose a dangerous amount of blood. When I wasn't on warfarin, I was on the alternative medication, heparin.
"One side effect of taking warfarin was the bruising. You become so sensitive; small bumps give you massive bruises and if you cut your skin, you bleed a lot. Small chores, like peeling potatoes, became quite a hassle.
"I came off warfarin after a year and after battling non-Hodgkin lymphoma I was diagnosed with cancer in my thyroid and bowel. During treatment for thyroid and bowel cancer, my second DVT was diagnosed. The clot was in my right leg again, but this time it was really painful – it felt like someone was sticking a needle into my calf muscle. The pain passed, but I think this clot may have caused more lasting damage. I still get pains in that leg, especially when I'm sitting down or when I have my feet up.
"I'm very aware that DVT is a risk for me now more than ever, and I know that one day I may have to take warfarin again, maybe even permanently. But I don't let the idea get me down. I just feel very lucky to be alive.
"In all my treatment for cancer and DVT, the biggest thing I've learned and the best advice I could give others is to stay positive and be as informed as you can be. Don't be afraid to ask questions."