Deep Vein Thrombosis (DVT)

Overview

Deep vein thrombosis, usually called DVT, is when a blood clot forms inside one of the deep veins in your body. These deep veins sit far below the skin's surface, most often in the legs — in the calf, thigh, or pelvis. A blood clot is like a thick, jelly-like lump that forms when blood pools and starts to solidify. While your body needs clotting to stop bleeding from a cut, a clot forming inside a vein without a reason can be harmful. DVT needs to be taken seriously because the clot can block blood flow, and in some cases it can break off and travel to the lungs, which is a medical emergency.

DVT is more common than many people realise. In the UK, it is estimated that around 1 in every 1,000 people develops a DVT each year. It affects people of all ages, though it becomes more common as you get older. It is one of the leading causes of preventable death in hospital patients worldwide.

DVT can affect anyone, but it is more likely in people who have been recently hospitalised, had surgery, are pregnant, are older, have certain medical conditions, or have spent long periods sitting still — such as on a long flight or car journey. People with a family history of blood clots or certain inherited conditions that affect clotting are also at higher risk.

Symptoms

Common symptoms

• Swelling in one leg (or arm, if the clot is there) — often noticeable compared to the other limb
• Pain or tenderness in the leg, which may feel like cramping or a dull ache — often starting in the calf
• Skin that feels warm or hot to the touch around the affected area
• Redness or a change in skin colour over the swollen area
• A feeling of heaviness or tightness in the leg

Symptoms in children

• Swelling in a limb that appears suddenly and without an obvious injury
• Unexplained pain or tenderness in an arm or leg
• Skin that looks red or feels warm over one spot on a limb
• Note: DVT is much less common in children, but it does happen — especially in children with serious illnesses, central venous lines (tubes placed in large veins for medical treatment), or inherited clotting conditions

Symptoms in older adults

• Symptoms in older adults are often the same as in younger people, but may be less obvious or may be mistaken for other conditions like arthritis or muscle strains
• Swelling in the leg that does not go away with rest or elevation
• Ongoing aching or heaviness in one leg that is different from usual
• Skin changes in the leg, such as redness or a bluish tint
• It is worth noting that up to half of people with DVT have no symptoms at all — this is why awareness of risk factors is so important

Causes

Main causes

• Slow or reduced blood flow in the veins — blood that moves slowly is more likely to pool and clot
• Damage or injury to the inner lining of a vein — this can trigger the clotting process
• Changes in blood chemistry that make it clot more easily than normal — this can be caused by illness, pregnancy, or inherited conditions
• These three factors (slow flow, vein damage, and clotting changes) are sometimes called Virchow's triad — named after the doctor who first described them

Risk factors

• Recent surgery — especially hip, knee, or abdominal surgery — because it can damage veins and reduce movement
• Long periods of immobility — such as long-haul flights, bed rest, or sitting at a desk for many hours without moving
• Hospitalisation or serious illness, especially when mobility is limited
• Pregnancy and the period after giving birth — because pregnancy increases pressure on leg veins and changes blood clotting
• Use of hormonal treatments — such as the combined contraceptive pill or hormone replacement therapy (HRT)
• Older age — the risk increases with age
• Being overweight or obese — this puts extra pressure on leg veins
• Smoking — it damages blood vessel walls and affects circulation
• Cancer and its treatments — certain cancers and chemotherapy increase clotting risk
• Inherited clotting disorders — conditions that run in families and make blood clot more easily than normal
• Previous DVT or a family history of DVT or pulmonary embolism
• Varicose veins (swollen, twisted surface veins) — these increase risk slightly
• Inflammatory conditions such as inflammatory bowel disease or lupus
• Heart failure or other conditions that slow circulation

When to see a doctor

See a doctor urgently if:

• You notice unexplained swelling, pain, redness, or warmth in one leg or arm — see a doctor the same day
• You have recently had surgery, been on a long journey, or have known risk factors and develop any leg symptoms
• You are pregnant or recently gave birth and notice leg swelling or pain that seems unusual
• Any leg symptoms alongside breathing problems — call emergency services right away, do not wait for a GP appointment

Book a routine appointment if:

• You want to discuss your personal risk of DVT before a long journey, surgery, or hospital stay
• You have a family history of blood clots and would like advice on whether you need further assessment
• You have had a DVT in the past and want to understand your ongoing risk and how to manage it
• You have questions about how your current medications or contraceptive method might affect your clotting risk

Diagnosis

To diagnose DVT, your doctor will start by asking about your symptoms, your medical history, and any risk factors you have. They will examine the affected limb carefully. Because many DVT symptoms can look like other conditions, doctors use a combination of scoring tools, blood tests, and imaging scans to reach a diagnosis. In the UK, the NHS uses a structured assessment called the Wells score to estimate how likely it is that your symptoms are caused by a DVT — this helps guide which tests you need next.

Tests that may be done

• D-dimer blood test — D-dimer is a protein fragment released when a blood clot breaks down. A raised level suggests a clot may be present, but it can also be raised for many other reasons (like infection, pregnancy, or recent surgery), so it is usually used alongside other tests rather than on its own.
• Ultrasound scan of the leg (compression ultrasound) — this is the main test used to confirm DVT. A handheld device uses sound waves to create a picture of the veins and can show if a clot is present. It is painless, safe, and does not use radiation.
• Venography — an older test where a dye is injected into a vein and X-rays are taken. It is rarely used now but may be done in complex cases.
• CT scan or MRI — these may be used if a clot is suspected in an unusual location, such as the pelvis or abdomen, or if a pulmonary embolism is also suspected.
• Blood tests to check for underlying clotting disorders — these may be arranged after an initial DVT, especially in younger people or those with no obvious cause

What to expect at your appointment

If your doctor suspects DVT, you will usually be seen quickly — often the same day. The ultrasound scan is straightforward: a gel is applied to the skin and a small handheld device is moved over the area. You may feel a little pressure but it is not painful. Results are often available immediately. If DVT is confirmed, your care team will discuss treatment with you straight away. If the diagnosis is unclear, you may need a repeat scan after a few days. Throughout this process, the team will explain each step so you know what is happening and why.

Treatment

The main goals of DVT treatment are to stop the clot from getting bigger, to prevent it from breaking off and travelling to the lungs, to help your body dissolve the clot over time, and to reduce the risk of it coming back. Treatment is usually started as soon as DVT is confirmed — and sometimes even before, if the risk is high while waiting for test results. Most people with DVT can be treated at home or with short hospital stays, though some cases require closer monitoring in hospital.

Self-care at home

• Keep moving — walking regularly helps blood flow in your legs and actually reduces pain and swelling better than resting completely in bed
• Elevate (raise) the affected leg when sitting or lying down — prop it up on a pillow so it is higher than your hip level, to help reduce swelling
• Wear compression stockings if recommended by your healthcare team — these specially fitted stockings put gentle pressure on the leg to improve blood flow and reduce swelling. Your team will advise you on the right type and how long to wear them
• Stay well hydrated — drinking enough water helps keep blood flowing well
• Avoid standing or sitting still for long periods — if you must sit for a while, flex and point your feet regularly, and get up to walk around every hour if you can
• Avoid crossing your legs, which can restrict blood flow
• Do not smoke — smoking damages blood vessels and makes clotting more likely

Medical treatments

The main medical treatment for DVT involves anticoagulant medicines — sometimes called 'blood thinners.' These medicines do not actually thin the blood, but they help prevent the clot from growing and stop new clots from forming, giving your body time to break down the existing clot naturally. There are several types of anticoagulant medicines available, and your doctor will choose the most suitable one based on your individual situation, including factors like your other health conditions, kidney function, and whether you are pregnant. Some are given as injections under the skin, while others are taken as tablets. Treatment usually lasts for at least three months, but may be longer depending on the cause of your DVT and your ongoing risk. Your team will monitor you during treatment and adjust it as needed. In some cases — usually when a clot is very large or causing serious problems — more intensive treatment may be used to dissolve the clot more quickly. This is called thrombolysis (breaking down a clot with medicines delivered directly to it) and is only used in carefully selected situations because it carries a higher risk of bleeding.

When is surgery considered?

Surgery for DVT is rare, but it may be considered in very specific situations — for example, when a very large clot is causing severe symptoms and is not responding to other treatments, or when there is a serious risk to a limb. A procedure called thrombectomy (surgical removal of the clot) or catheter-directed treatment (using a thin tube to reach the clot and treat it directly) may be used in specialist vascular surgery centres. Your medical team will carefully weigh the benefits and risks before recommending any procedure. In some people at high risk of pulmonary embolism who cannot take anticoagulants, a small filter may be placed in a large vein to catch any clots before they reach the lungs — though this is not a treatment for DVT itself.

Living with this condition

Living with DVT, especially in the weeks and months after diagnosis, can take some adjustment — but most people get back to their normal lives with the right treatment and support. You may need to take anticoagulant medicine for several months and attend follow-up appointments. Some people experience ongoing swelling or discomfort in the affected leg — a condition called post-thrombotic syndrome (when the vein is damaged after a clot, causing long-term changes in blood flow). Compression stockings, regular walking, and keeping your leg elevated when resting can all help manage these symptoms. It is important to attend all your follow-up appointments so your team can monitor your progress and make sure your treatment is working well.

Lifestyle tips

• Stay as active as possible — regular walking is one of the best things you can do for your circulation and recovery
• If you have a job that involves sitting for long periods, take regular breaks to walk around and keep your legs moving
• On long journeys, get up and move around regularly, do leg exercises in your seat, and stay well hydrated
• Wear your compression stockings as directed by your healthcare team — they make a real difference to swelling and discomfort
• Maintain a healthy weight — this reduces pressure on your veins and lowers the risk of another clot
• Stop smoking if you smoke — your healthcare team can offer support and advice to help you quit
• Be mindful of activities that carry a high risk of injury or bleeding while you are taking anticoagulant medicines — speak to your team about what is safe for you
• Wear a medical alert bracelet or carry a card if recommended, to let others know you are on anticoagulant treatment in case of an emergency

Diet and exercise

Eating a balanced, healthy diet is good for your overall circulation and heart health. If you are taking certain types of anticoagulant medicine, your doctor may advise you about foods that can affect how the medicine works — for example, some anticoagulants are affected by large changes in the amount of vitamin K in your diet (found in green leafy vegetables like spinach and broccoli). Your healthcare team will give you specific guidance if this applies to you. In general, a varied, nutritious diet with plenty of vegetables, fruit, wholegrains, and lean proteins is beneficial. Exercise is actively encouraged — gentle walking, swimming, and cycling are excellent for improving circulation and overall wellbeing. Avoid sitting or lying still for extended periods whenever possible. If you are unsure what exercise is safe for you during treatment, ask your healthcare provider.

Mental health and emotional wellbeing

Being diagnosed with DVT — particularly if it came with a frightening experience like a pulmonary embolism — can have a real emotional impact. It is completely normal to feel anxious, frightened, or upset. Some people worry about having another clot, or feel frustrated by the changes a long course of treatment brings to daily life. If you are feeling persistently anxious, low in mood, or overwhelmed, please talk to your healthcare provider or a mental health professional. You are not alone in feeling this way, and support is available. If you are ever in emotional crisis, please reach out to a crisis support service in your area.

Prevention

Not all DVTs can be prevented, but there is a great deal you can do to lower your risk — especially in higher-risk situations. If you are going into hospital for surgery, your medical team will assess your DVT risk and may recommend preventive measures such as anticoagulant injections, compression stockings, or special inflatable leg cuffs that keep blood moving during and after your operation. It is important to get up and move as soon as safely possible after surgery. For long journeys, staying hydrated, wearing compression stockings, doing regular leg exercises, and walking around during the journey can all reduce risk. If you have risk factors for DVT, speak to your GP or specialist — they can help you understand your personal risk and what steps to take to protect yourself. If you are planning a long-haul flight and have had a previous DVT or other risk factors, seek medical advice before you travel.

Screening programmes

There is no routine population-wide screening programme for DVT. However, people with a strong family history of blood clots, or those who have had a DVT without a clear cause, may be offered blood tests to check for inherited clotting conditions (called thrombophilia testing). This can help your healthcare team understand your risk and plan the best approach to prevent future clots. If you think this might apply to you, speak to your GP or specialist.

Complications

If left untreated

• Pulmonary embolism (PE) — the most serious complication, where a piece of the clot breaks off and travels to the lungs. This can be life-threatening and is a medical emergency.
• Post-thrombotic syndrome — long-term damage to the vein caused by the clot, leading to ongoing swelling, pain, skin changes, and sometimes leg ulcers (open sores). This affects around one in three people after a DVT.
• Recurrent DVT — people who have had one DVT have a higher chance of developing another, especially if the underlying cause is not treated or if preventive measures are not taken.
• In rare and severe cases, a condition called phlegmasia (very severe clotting that blocks nearly all blood flow from the leg) can develop, which is a surgical emergency requiring urgent specialist treatment.

Long-term outlook

The outlook for DVT is genuinely encouraging when it is diagnosed and treated promptly. The vast majority of people with DVT recover well, return to their normal activities, and go on to live full, healthy lives. Treatment is effective at preventing pulmonary embolism and reducing the risk of further clots. Some people do experience longer-term symptoms in the affected leg, but these can usually be managed well with the right care. Your healthcare team will work with you to monitor your recovery, reduce your risk of recurrence, and support you every step of the way. If you have had a DVT, knowing the symptoms and risk factors means you are well placed to get help quickly if you ever need it again — and that knowledge is powerful.

Find support

International organisations

• International Society on Thrombosis and Haemostasis (ISTH) — patient information ↗
• Thrombosis Research Institute — patient resources ↗
• World Thrombosis Day — patient education and awareness ↗

Local organisations

• NHS — Deep vein thrombosis (DVT) information ↗ · United Kingdom
• Thrombosis UK — patient support and information ↗ · United Kingdom
• Centers for Disease Control and Prevention (CDC) — DVT information ↗ · United States
• National Blood Clot Alliance (NBCA) — Stop the Clot ↗ · United States
• Lifeblood: The Thrombosis Charity (Australia) ↗ · Australia

Helplines

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