Deep Vein Thrombosis (DVT)

What happens in DVT

Veins carry blood back to the heart. Deep veins run through the muscles of the legs, pelvis and arms. A clot forms when three factors combine, known as Virchow's triad:

1. Slow blood flow: immobility, long journeys, paralysis, heart failure
2. Vessel wall injury: surgery, trauma, catheters
3. Blood that clots more easily: cancer, pregnancy, estrogen, inherited disorders, inflammation

The clot can partly or completely block the vein, causing swelling. If a piece breaks free, it travels through the heart to the lungs as a pulmonary embolism (PE). DVT and PE together are called venous thromboembolism (VTE).

DVT symptoms

• swelling of one leg, ankle or calf, often noticeable when one sock feels tighter
• pain or tenderness in the calf or thigh, often described as a cramp or ache, worse when standing or walking
• warmth over the area
• red or discolored skin
• visible surface veins

Up to half of DVTs cause few or no symptoms. Clots in both legs at once are uncommon.

Signs of pulmonary embolism

• sudden breathlessness
• chest pain, often sharp and worse when breathing in
• coughing up blood
• fast heartbeat, light-headedness or collapse

PE is a medical emergency: call 911 or your local emergency number.

DVT vs other causes of leg pain and swelling

Only an ultrasound can reliably rule DVT in or out.

Risk factors

For clots after operations, see postoperative thrombosis. For pregnancy, see pregnancy thrombosis.

How DVT is diagnosed

1. Clinical probability score (Wells score): points for risk factors, symptoms and whether another diagnosis is more likely.
2. D-dimer blood test: measures a breakdown product of clots. A normal result in someone at low probability makes DVT very unlikely. It is often raised for other reasons, such as pregnancy, surgery, infection or older age, so a high result is not diagnostic.
3. Compression ultrasound: the main test. A vein that cannot be squashed by the probe contains a clot. It is quick, painless and uses no radiation.
4. CT or MR venography for clots in the pelvis or abdomen.
5. CT pulmonary angiogram if PE is suspected.

After a first unprovoked clot, doctors may check for cancer through history, examination and routine tests, and occasionally test for inherited clotting disorders.

DVT treatment

Anticoagulants

Blood thinners stop the clot from growing and prevent new clots while the body gradually dissolves the existing one. They do not dissolve the clot directly.

• Direct oral anticoagulants (DOACs) such as apixaban and rivaroxaban are first-line for most people.
• Low-molecular-weight heparin injections are used in pregnancy and sometimes in cancer.
• Warfarin needs regular INR blood tests and is used in some situations, such as antiphospholipid syndrome or mechanical heart valves.

Most people can be treated at home. Treatment usually lasts at least 3 months. After a clot with a temporary cause, such as surgery, 3 months is often enough. After an unprovoked clot or with ongoing risk factors, long-term treatment may be recommended.

Bleeding is the main risk. Seek help for black stools, vomiting blood, blood in urine, severe headache or bleeding that will not stop.

Other treatments

• Compression stockings may ease swelling and pain; they are not routinely needed to prevent post-thrombotic syndrome.
• Walking is encouraged once anticoagulation starts.
• Clot-dissolving drugs or catheter procedures for selected extensive clots that threaten the limb.
• IVC filter (a device in the large abdominal vein) only for people who cannot take anticoagulants.

Complications

• Pulmonary embolism
• Post-thrombotic syndrome: long-term leg pain, swelling, heaviness, skin discoloration and ulcers, affecting a significant proportion of people after a leg DVT
• Recurrent DVT
• Chronic thromboembolic pulmonary hypertension, a rare complication of PE

Prevention

• move and walk as soon as possible after surgery or illness
• in hospital, preventive blood thinners or compression devices may be given based on risk
• on long trips, walk every 1 to 2 hours, flex your calf muscles, drink fluids, and avoid alcohol and sleeping pills. Those at higher risk may be advised to wear compression stockings
• maintain a healthy weight and stop smoking
• discuss clot risk before starting estrogen-containing contraception or hormone therapy

Frequently asked questions

What are the first signs of a DVT?

Common early signs are swelling in one leg or calf, aching or cramp-like pain, tenderness, warmth and redness of the skin. Some DVTs cause no symptoms until a pulmonary embolism occurs. Any new one-sided leg swelling and pain should be checked promptly.

How is a DVT diagnosed?

Doctors use a clinical probability score and often a D-dimer blood test. If DVT is possible, a compression ultrasound of the leg veins confirms or rules it out. CT scans are used if a lung clot is suspected.

How long does it take for a DVT to go away?

Symptoms usually improve within days to weeks of starting blood thinners. The clot itself shrinks over weeks to months as the body breaks it down. Anticoagulants are typically taken for at least 3 months, sometimes longer.

Can you walk with a DVT?

Yes. Once anticoagulant treatment has started, walking is encouraged and does not increase the risk of the clot moving. It helps reduce swelling and pain. Follow your doctor's advice.

What is the difference between DVT and a pulmonary embolism?

A DVT is a clot in a deep vein, usually in the leg. A pulmonary embolism happens when part of a clot breaks off and blocks an artery in the lungs, causing breathlessness and chest pain. PE is a medical emergency.