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Recognising and treating thrombosis

When a blood clot closes a vessel, doctors call it thrombosis. This occurs particularly frequently in the leg veins, but other vessels in the body may also be affected. Thrombosis is dangerous because the clot (the thrombus) can detach at any time and be carried by the blood to various organs, where it can lead to a blockage and cut off the blood supply from the area behind the occlusion. Find out which signs are characteristic of thrombosis, which treatments are available and how to prevent it.


The term thrombosis is derived from the Latin term “thrombus”, which means plug or lump. It is a kind of vascular occlusion (closure), e.g. of a vein that supplies blood to the heart. In principle, a blood clot can form in all vessels of the body, but this mainly occurs in the deeper veins of the lower leg (deep vein thrombosis) or the thigh. It can also occur in the pelvic area or in the arms. A distinction is made between venous and arterial thrombosis.

A thrombus may dislodge in whole or in part and enter the lungs via the heart. This is dangerous because the clot can clog the blood vessels in the lungs, which are vital for breathing. This condition is known as pulmonary embolism. The larger the clot, the higher the risk.

Thrombosis often forms in the lower leg and exhibits typical signs, but these may manifest differently depending on the region and size of the blood clot.

Common symptoms of leg thrombosis include:

  • Swelling in the affected area, e.g. calf or ankle
  • Water retention
  • Feeling of pressure or tension
  • Muscle aches, potentially up to convulsions
  • Blue colouring of the skin
  • Protruding veins
  • Warm areas of skin, reddening

There are different treatment methods, which can be used alone or in combination, depending on the location of the thrombosis. The aim is always to prevent the detachment of a blood clot, as this can otherwise lead to an embolism (blood clot blocking a vessel) in organs such as the lungs.

In the case of acute thrombosis of the extremities, a compression bandage is usually applied first. It is applied very tightly to increase the pressure on the veins and improve blood flow. This also reduces possible swelling. At the same time, the affected arm or leg is raised.

Thrombosis is also treated with medication. The same drugs are used for thrombosis as for prophylaxis. Known as anticoagulants, these medicines inhibit blood clotting. Usually, the active substance heparin is injected under the skin or given intravenously. After treatment, patients are advised to take anticoagulant medication in tablet form for a few months. This is intended to prevent a recurrence of thrombosis.

Depending on the situation, further treatment options are surgically removing the thrombus (thrombectomy) or dissolving it with medication (thrombolysis).

There are various reasons why blood clots form in blood vessels. Often, they do so for a combination of reasons. On the one hand, the speed at which blood flows through the vein may be slower than normal. There are several possible reasons for this, such as dehydration, which causes the blood to thicken, varicose veins (enlarged veins) or insufficient muscle tone. On the other hand, a propensity for blood clotting may trigger thrombosis. This is due to certain diseases such as cancer, but also to certain medications (birth control pills) or smoking. Damage or constriction of the vascular wall should also be considered, e.g. due to deposits, tumours or scarring.

Other factors that may increase the risk of thrombosis include:

  • Old age
  • Genetic predisposition
  • Heart failure
  • Obesity
  • Severe varicose veins
  • Hormone intake
  • Frequent air travel with long periods of sitting
  • Several restricted mobility or immobility

The main way to prevent a blood clot is to reduce the risk factors. For everyday life, this means avoiding long periods of sitting and making sure that you get plenty of exercise. Ensure sufficient fluid intake and reduce cigarette smoking. In order to promote circulation, e.g. in the lower leg, small exercises such as tapping your foot may be useful.
Arms or legs are often immobilised after surgery or injury. In such cases, a heparin injection may prevent thrombosis.

Compression stockings can also help. They usually extend over the knee but sometimes include the thigh. These stockings are made of an elastic material that puts pressure on the veins and speeds up the flow of blood. Thrombosis can often be avoided in this way, especially on long flights and for those individuals with a history of varicose veins.

Because the symptoms alone are not a certain indicator for an accurate diagnosis, doctors usually perform a blood test (D-dimer test). If a blood clot is present, this can be detected via substances that the body produces when a blood clot occurs.

If the result is positive, a duplex ultrasound is usually used to confirm the diagnosis. This provides further information about the state of the deep veins in the legs and the blood flow in them. If the suspicion of thrombosis is confirmed, an ultrasound examination is also performed.

In rare cases, an X-ray examination of the vessels is necessary, in which a contrast medium is injected into the vein via a catheter to make the thrombosis visible.

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