Deep vein thrombosis (DVT)

Deep vein thrombosis occurs when a blood clot forms in the veins. The symptoms are tenderness, red skin or swelling of the lower leg. Read the article to find out what causes it and how it can be treated.

At a glance

  • Deep vein thrombosis (DVT) often goes unnoticed and dissolves on its own.
  • If someone is diagnosed with DVT, they will need treatment to avoid serious complications such as pulmonary embolism.
  • Studies have estimated that an average of about 1 out of 1,000 people develop noticeable (symptom-causing) deep vein thrombosis per year.

Note: The information in this article cannot and should not replace a medical consultation and must not be used for self-diagnosis or treatment.

Eine ältere Fau zieht sich einen Kompressionsstrumpf über ein Bein. Am anderen Bein ist bereits ein Strumpf

What is deep vein thrombosis?

In a thrombosis, a blood clot blocks a blood vessel. In deep vein thrombosis (DVT), the blood clot forms in one of the larger, deeper veins that run through the muscles. Deep vein thrombosis usually occurs in the lower leg.

It often goes unnoticed and dissolves on its own. But it may cause symptoms like pain and swelling. If someone is diagnosed with deep vein thrombosis, they will need treatment to avoid serious complications such as pulmonary embolism. This can occur if the blood clot breaks away from its original site and is carried to the lungs in the bloodstream.

The risk of deep vein thrombosis increases after major operations such as knee or hip replacement surgery. Because of this, people who have had this kind of surgery are usually given medication to prevent blood clots from forming.

What is pulmonary embolism?

The video below explains more about the symptoms, risk factors and treatment options for pulmonary embolism.

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What are the symptoms of deep vein thrombosis?

Typical symptoms of deep vein thrombosis (DVT) include pain in a leg or hip. Common symptoms also include tenderness, tightness and red skin. The affected area may also swell and feel warm. But sometimes DVT doesn't cause any symptoms.

What causes deep vein thrombosis?

Blood clots may form if the blood flow in a vein is too slow, if there is a blood clotting disorder, or if the wall of a blood vessel is damaged.

This can happen in the following cases:

  • After longer periods of bed rest, for instance in hospital, after a bone fracture or injury: staying in bed for a long time and not moving much can lead to poor blood circulation in the legs.
  • Blood clotting disorders: some people are born with a disease that makes their blood clot too much.
  • Major surgery and injuries: major surgical procedures and serious injuries cause damage to blood vessels and activate the blood clotting (coagulation) system.
Für eine Venenthrombose gibt es verschiedene Ursachen: eine längere Bettruhe, etwa im Krankenhaus, Blutgerinnungsstörungen, größere Operationen und Verletzungen.

Which factors increase the risk of deep vein thrombosis?

There are also various other factors that can increase someone's risk of developing DVT, including

Taken on their own, however, most of these risk factors only very slightly increase the risk of DVT.

How common is deep vein thrombosis?

Studies have estimated that an average of about 1 out of 1,000 people develop noticeable (symptom-causing) deep vein thrombosis per year. The risk increases with age. It is somewhat more common in men than in women.

Approximately 1 out of every 1,000 people develops painful deep vein thrombosis every year.

What are the potential complications of deep vein thrombosis?

One complication of DVT known as “post-thrombotic syndrome” is not uncommon and occurs a few weeks or months after thrombosis. It can develop if the thrombosis has damaged the walls or valves of a vein, causing the blood to constantly build up in the vein.

The signs of PTS are a swollen leg that feels heavy and hurts. The skin on their leg may also become discolored and itch, and a rash may develop. More severe cases of post-thrombotic syndrome can lead to the formation of a chronic wound.

How can deep vein thrombosis be prevented?

There are different ways to try to prevent deep vein thrombosis (DVT). If someone has had surgery or was injured and has to stay in bed for a few days, it is important that they get up and start moving again as soon as possible. Even small movements like wiggling the feet are recommended in order to improve circulation.

If someone has an increased risk of deep vein thrombosis it can be a good idea for them to wear compression stockings. These special stockings apply pressure to the legs due to their tight fit, which helps the blood flow back to the heart faster and reduces the risk of DVT.

Another option is medication that reduces the clotting ability of the blood. This can be injected or swallowed. Medications that are injected into the skin or a vein already start working after a few hours. Examples include medications known as heparins and the active substance fondaparinux.

There are two main kinds of oral medications, known as coumarins and direct oral anticoagulants (DOACs). The best known active agent from the group of coumarins is called phenprocoumon, known by many under the trade name Marcumar or Marcoumar. Examples of DOAC drugs include apixaban, dabigatran, edoxaban and rivaroxaban. Coumarins only start working after a few days, while direct oral anticoagulants already start working after a few hours.

To find out when it is a good idea to prevent deep vein thrombosis with anti-thrombotic injections, visit

How is deep vein thrombosis diagnosed?

Deep vein thrombosis cannot be diagnosed for sure based on typical symptoms alone. Symptoms such as pain, swelling and red skin can be caused by other conditions too, including an inflammation of superficial veins, varicose veins, erysipelas or narrow leg arteries (peripheral artery disease, or PAD).

To diagnose DVT, a blood test called a D-dimer test is usually done first. This test reacts to substances that are released when blood clots are broken down. The substances are called D-dimers. If the results of the test are normal, doctors can be quite sure that the person does not have DVT. If the results are abnormal, a special kind of ultrasound scan (a Doppler ultrasound) is done in order to confirm the diagnosis. Doppler ultrasounds provide the doctor with information about the condition of the deep veins and blood flow in the veins.

If there’s good reason to believe that someone has DVT, an ultrasound scan is usually done immediately. Examinations involving a small procedure are only rarely needed. One example is a special x-ray examination of the blood vessels which helps to see if there are any narrow areas (angiography). This involves injecting a contrast medium into the vein using a catheter.

How can deep vein thrombosis be treated?

Deep vein thrombosis is usually treated in a hospital over several days, using the same medications that are used to prevent thrombosis. The treatment is started with a medication that works quickly, such as heparin.

To make sure that the blood clot dissolves completely, patients are advised to take anticoagulant (anti-clotting) tablets for three months after having acute treatment. Sometimes it can be a good idea to take them for even longer.

For people who can’t take anticoagulants, an alternative option is having a small metal filter (known as an “inferior vena cava filter” or “IVC filter”) implanted in the large vein above the kidney. The filter is meant to catch any blood clots that could otherwise travel from the leg to the lungs. It is implanted using a venous catheter, in a procedure similar to cardiac (heart) catheterization.

The risk of post-thrombotic syndrome can be lowered by wearing compression stockings for up to two years.

In cooperation with the Institute for Quality and Efficiency in Health Care (Institut für Qualität und Wirtschaftlichkeit im Gesundheitswesen) (IQWiG).

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