Venous thrombosis (DVT)

A deep vein thrombosis (DVT) is a blood clot in one of the deep veins, usually in the calf or thigh, and sometimes in the pelvis or arm. The clot partly or fully blocks the vein, so blood struggles to return from the leg. This causes swelling, pain and warmth.

A DVT needs prompt diagnosis for two reasons. First, part of the clot can break off and travel to the lungs. This is called a pulmonary embolism and can be life-threatening. Second, a clot can damage the valves inside the vein, leading to long-term swelling, aching and skin changes known as post-thrombotic syndrome.

With early treatment, most people recover well.

Clots form when blood flows slowly, when the vein wall is injured, or when the blood clots more easily than usual. Common risk factors include:

Recent surgery, especially hip, knee or abdominal operations

Being in bed or immobile for a long time, or a leg in plaster

Long journeys by plane, car or bus

Pregnancy and the weeks after giving birth

Hormonal contraceptive pills or hormone replacement therapy

Cancer and its treatment

A previous clot, or a family history of clots

Being overweight, dehydration or smoking

Sometimes no clear cause is found. In that case your doctor may suggest further tests.

The doctor asks when the symptoms started and about recent surgery, travel, illness or medicines, then examines both legs.

The main test is a duplex Doppler scan of the leg veins. It is painless, uses no radiation and usually gives an answer at the same visit. The scan shows whether there is a clot, how far it extends and whether it is in the deep or surface veins.

A blood test called D-dimer (which rises when the body is breaking down a clot) may also be used, mainly to help rule a clot out. If you have breathlessness or chest pain, further tests for a lung clot are needed urgently. Bring any previous scans, blood tests and your current medicines.

Most DVTs are treated with medicines, without any procedure:

Anticoagulants (blood thinners): these stop the clot growing and new clots forming while the body slowly dissolves the existing one. They are usually taken for at least three months, and sometimes longer depending on the cause. Tablets or injections may be used.

Compression stockings: these can ease swelling and aching once treatment has started; your doctor will advise if they suit you.

Catheter-directed treatment: for selected patients with a large clot in the main thigh or pelvic veins, a catheter is passed into the clot to dissolve it with medicine (thrombolysis) or remove it. This aims to relieve severe symptoms and reduce long-term damage to the vein.

Walking is usually encouraged once treatment has started.

Pain and swelling usually improve over days to weeks after starting a blood thinner. Some swelling can last longer, especially towards the end of the day.

Take your blood thinner exactly as prescribed and do not stop it without advice. Tell any doctor or dentist that you take it, and report unusual bleeding, such as blood in the urine or black stools.

A follow-up visit, often with a repeat scan, helps decide how long treatment should continue. Some people develop post-thrombotic syndrome, with lasting heaviness, swelling or skin changes. Staying active, raising the leg when resting and, if advised, wearing compression stockings help. If you have had a clot, ask about protection before future surgery, long travel or pregnancy.

A suspected DVT should be checked the same day. Contact the clinic or a doctor promptly if you have:

Swelling of one leg, especially if it came on over hours or days

Pain, tenderness or cramping in the calf or thigh

Warm, red or discoloured skin on the leg

Any of these after surgery, a long journey, a period of bed rest, or during pregnancy

Call an ambulance or go to the emergency department straight away if you have:

Sudden shortness of breath

Chest pain, especially when breathing in

Coughing up blood

Fainting, a racing heart or feeling very unwell

A leg that becomes massively swollen, blue and very painful