Thrombosis is the formation of a blood clot (thrombus) in a blood vessel that obstructs or completely blocks blood flow. There are two main types of thrombosis: venous and arterial thrombosis, which differ significantly in their development, typical locations, symptoms and treatment.
Thrombosis at a glance
Venous thrombosis
Venous thrombosis is the formation of a blood clot (thrombus) in a vein that partially or completely blocks blood flow. It most commonly occurs in the deep veins of the leg or pelvis (deep vein thrombosis, DVT). If part of the clot breaks loose, it can enter the lungs and cause a pulmonary embolism, the most dangerous complication of venous thrombosis.
Arterial thrombosis
In contrast to venous thrombosis, arterial thrombosis occurs in the arteries, i.e. the blood vessels that carry oxygen-rich blood from the heart to the body. They are usually caused by arteriosclerosis (hardening of the arteries), in which connective tissue, blood lipids, and calcium build up in the artery walls, causing them to narrow. If one of these deposits (plaques) ruptures, a thrombus can form at this site, suddenly blocking the vessel. The consequences of arterial thrombosis depend on which organ is affected. A thrombosis in the heart can trigger a heart attack, while in the brain it can cause a stroke.
Causes of thrombosis
When discussing the causes of thrombosis, it’s important to distinguish whether the blood clot originated in a vein or in an artery. Generally speaking, however, the risk of thrombosis increases significantly with age. While only about 1 in 10 000 people between the ages of 20 and 40 are affected every year, around 1 in 100 people over 75 are affected yearly.
Causes of venous thrombosis
Thrombosis usually occurs in a vein when several risk factors come together. These include changes to or damage to the vessel wall, a slowdown in blood flow and an increased tendency to form clots.
Slowed blood flow
If the blood flows more slowly over a longer period, the risk of clots forming increases. This can happen, for example, when sitting for a long time while travelling, after surgery, when bedridden or due to a lack of exercise.
Damage to the vessel wall
Injuries or irritations of the vein wall can also encourage the formation of blood clots in the veins, for example after surgery, accidents, inflammation or even from varicose veins.
Change in blood coagulation
If blood clotting increases, the blood tends to form clots more quickly. Triggers include genetic clotting disorders, cancer, certain medications (e.g. hormonal contraception) or pregnancy.
In addition, other risk factors can promote venous thrombosis, including:
- Advanced age
- Being overweight
- Smoking
- Family history
- Serious illnesses such as heart failure or tumours
Causes of arterial thrombosis
Arterial thrombosis can have various causes. However, in most cases, the primary cause is arteriosclerosis. Changes in blood composition and other interacting risk factors can also increase the risk of arterial thrombosis.
Vascular changes (arteriosclerosis)
The most common cause of arterial thrombosis is arteriosclerosis, where connective tissue, fat and calcium deposits accumulate in the vessel wall. This develops over years and is accelerated by adverse lifestyles factors such as a high-fat diet, lack of exercise and smoking.
Changed blood composition
High blood lipid levels, diabetes mellitus or increased platelet activity promote the formation of clots and can therefore also increase the risk of developing a thrombus. In venous thrombosis, on the other hand, an increased tendency of the blood itself to clot (e.g. due to genetic disorders, cancer or hormones) plays a role.
Other risk factors
In the case of arterial thrombosis, several risk factors often interact and exacerbate each other. The more of these factors that are present, the higher the probability that arterial thrombosis will develop:
- High blood pressure
- Smoking
- Being overweight
- Lack of exercise
- Advanced age
- Chronic inflammation
- Family history of cardiovascular disease
Symptoms
The symptoms of thrombosis are not always clear and can vary greatly. It depends on how far it has already progressed and on which form of thrombosis has occurred.
Signs of deep vein thrombosis
Typical signs of deep vein thrombosis include:
- Feeling of heaviness or tightness in the legs
- Swelling in the lower legs
- A feeling of warmth in the affected region
- Discolouration and redness in the affected area
- Pain in the calf or back of knee
However, these symptoms are non-specific and can also occur with other illnesses. However, if they occur immediately after an surgery, a long flight or a period of being bedridden, a doctor should be consulted immediately.
It is also important to distinguish thrombosis from varicose veins. Varicose veins are caused by damaged venous valves, which cause the blood to flow back into superficial veins. This is a much less dangerous condition. In contrast, deep vein thrombosis carries the risk of a blood clot breaking away and moving into the lungs, where it can cause pulmonary embolism.
Signs of a pulmonary embolism
If a thrombosis remains untreated, the blood clot can beak free, travel with the bloodstream and enter the lungs. Minor pulmonary embolisms often only cause shortness of breath during physical exertion or initially go unnoticed. However, if several large blood vessels are affected, shortness of breath can also occur at rest, in which case emergency services must be called immediately. Other possible symptoms of pulmonary embolism include breathing-related chest pain, coughing up blood, fever or even loss of consciousness.
Signs of arterial thrombosis
The symptoms of arterial thrombosis are usually sudden and depend heavily on which organ is affected. As these are often acute emergencies, immediate medical assessment is crucial.
Signs of a stroke
Signs of a stroke can vary greatly. Do not hesitate to call emergency services if any of the following symptoms occur suddenly:
- Speech, visual or movement disorders
- One-sided numbness, tingling or paralysis
- Sudden dizziness
- Sudden onset of very severe headaches
Signs of a heart attack
A heart attack (myocardial infarction) is always an emergency. It is therefore crucial to recognise the symptoms quickly. Typical signs are:
- Severe, pressing or burning chest pain radiating to the arm, back or jaw
- Shortness of breath and severe anxiety
- Accompanying symptoms such as pale facial colour, nausea, weakness, sweating or irregular pulse
Diagnosis
Diagnosing venous thrombosis
If deep vein thrombosis is suspected, the doctor first examines the affected area and looks for typical signs such as swelling, redness or excessive warmth. Additional blood tests are then carried out (e.g. D-dimer test). The final diagnosis is usually made by a special ultrasound examination known as Doppler ultrasonography.
Diagnosing arterial thrombosis
If arterial thrombosis is suspected, various imaging techniques are used. These include, for example, electrocardiograms and cardiac ultrasound if a heart attack is suspected, and CT or MRI brain examinations if a stroke is suspected. Blood tests are usually also carried out (e.g. D-dimer test or identifying heart attack markers such as troponin).
Treatment
Treatment for venous thrombosis
In the case of thrombosis that is localised in a vein (e.g. deep vein thrombosis), anticoagulation is the primary treatment method. In the acute stage, the anticoagulant medications are administered as injections, and then in tablet form. Compression stockings support blood circulation, and exercise instead of bed rest also helps to increase blood flow.
If the venous thrombosis has already developed into a pulmonary embolism, treatment with anticoagulants is also performed. In severe cases, the blood clot can also be dissolved with medication (lysis therapy) or, if necessary, surgically removed.
Treatment of arterial thrombosis
In the case of arterial thrombosis, the focus is on rapidly reopening the affected vessel. In the case of a heart attack, a cardiac catheter examination with dilation and stent insertion is usually carried out immediately. In the event of a stroke, the clot is dissolved with medication or mechanically removed, depending on the situation. The patient is then given antiplatelet medication to prevent a new clot.
Prevention
Thrombosis cannot always be prevented, but the risk can be significantly reduced. It is important to get enough exercise, eat a balanced diet and avoid risk factors such as smoking or being severely overweight. If you sit for long periods, for example when travelling or in the office, you should get up regularly or move your legs. Adequate hydration also supports blood flow. After surgery or in case of increased risk, compression stockings and, if prescribed by a doctor, anticoagulants can be used as a preventive measure. It is also useful to have your blood pressure, blood sugar and cholesterol checked regularly in order to detect vascular diseases at an early stage.
Questions about thrombosis
Is thrombosis dangerous?
Yes, thrombosis can be dangerous. If the blood clot (thrombus) breaks loose and travels with the bloodstream, it can block vital vessels.
Can thrombosis be prevented?
Complete prevention is not always possible, but the risk can be significantly reduced. Important measures include daily exercise, drinking enough fluids, not smoking and, for high-risk patients, wearing compression stockings or taking blood thinners as recommended by a doctor. To prevent arterial thrombosis, it is also important to regularly monitor blood pressure, blood sugar and cholesterol.
How do I recognise the symptoms of thrombosis?
Typical signs of venous thrombosis are pain or tightness in the leg, swelling, redness or the skin feeling excessively warm. Some patients also notice a bluish discolouration.
Arterial thrombosis usually manifests as sudden, severe pain, paleness or coldness in the arm or leg. If the heart or brain is affected, typical signs of a heart attack, such as chest pain, or a stroke, such as paralysis, speech or vision problems, may occur.
What are the most common complications of thrombosis?
The most serious consequences of thrombosis are pulmonary embolism, heart attack or stroke. If thrombosis is suspected, a doctor should be consulted immediately.
How is thrombosis treated?
Treatment depends on the type of thrombosis. Venous thrombosis is usually treated with anticoagulants that prevent blood clots from getting bigger or new ones from forming. In addition, compression stockings are often recommended to support blood circulation.
Arterial thrombosis must be treated as quickly as possible, usually by reopening the blocked vessel, for example by means of a catheter, stent or lysis therapy. After that, patients usually receive antiplatelet drugs to prevent new thrombus formation.
