June 9, 2026, 6:51 pm | Read time: 5 minutes

How Dangerous a Thrombosis Can Be

A thrombosis can generally occur in veins (vessels to the heart) or arteries (vessels from the heart), with the proportion of venous thromboses being significantly higher. A distinction is made between superficial and deep vein thrombosis. The deep form usually affects the leg veins, less commonly the pelvic or arm veins.

A thrombosis (also called a blood clot) can also form in arteries. In this case, it is referred to as an arterial thrombosis. This is particularly dangerous in the coronary arteries, as it can lead to a heart attack, or in the cerebral arteries, as a blockage here can trigger a stroke.¹

A thrombosis becomes particularly dangerous when a part of the blood clot breaks off and travels through the heart to the lungs. There, it can block a vessel and cause a life-threatening pulmonary embolism. Therefore, even seemingly minor signs should be taken seriously.

Typical Thrombosis Symptoms

A deep vein thrombosis does not always manifest clearly. Some affected individuals initially experience only mild discomfort, while others show no signs at all. This is what makes the condition so insidious: It often becomes noticeable only when a complication occurs. There is no single specific symptom, but rather a variety of possible warning signs:²

• sudden swelling
• feeling of tension or heaviness
• pain
• bluish discoloration of the skin
• unusual warmth
• prominent veins

A hardened and tender cord under the skin can indicate a superficial vein thrombosis. This is located directly under the skin and is usually accompanied by inflammation of the vessel. Although it is less dangerous than a deep thrombosis, it should not be underestimated: The clot can spread to the deeper venous system.

Symptoms such as shortness of breath, sudden chest pain, or an unusually rapid pulse should be taken particularly seriously. They can indicate an advanced stage of the disease and thus already point to a pulmonary embolism.

Also of interest: How can you prevent thrombosis while flying?

How a Thrombosis Is Diagnosed

Whether a thrombosis is present or can be ruled out is usually reliably determined with an ultrasound examination. The standard procedure is the so-called compression sonography. In this process, the treating phlebologist presses the ultrasound probe on the affected veins. Healthy, unobstructed veins can be completely compressed. However, if a blood clot is present in the vessel, the vein cannot be compressed or only to a limited extent.

Additionally, color-coded duplex sonography is often used. It makes the blood flow in the veins visible and shows possible narrowings. Only in exceptional cases are further imaging procedures such as computed tomography (CT) or magnetic resonance imaging (MRI) considered–for example, when determining the exact extent of a thrombosis in the pelvic area.³

How Thromboses Are Treated

In the case of an acute thrombosis, the primary focus is on quickly preventing further growth of the blood clot. Patients receive an anticoagulant medication, which is injected under the skin. It ensures that the clot does not grow further, thus reducing the risk of a pulmonary embolism. At the same time, an early start of therapy improves the chance that the body will dissolve the thrombus on its own. This often helps prevent permanent vein damage and subsequent diseases.

After a confirmed diagnosis and initial therapy, blood thinners are used as maintenance therapy to prevent further growth of the clot and reduce the risk of a recurrent thrombosis. This therapy, usually administered with tablets, often needs to be continued for several months. In addition to blood thinning, compression therapy of the affected limb is also important. It alleviates pain and swelling in the acute stage and supports blood flow in the veins.

In rare cases, the clot can be specifically dissolved in the first few hours (thrombolysis). However, this procedure is only considered in exceptional cases. Surgical removal is also only considered in special cases.

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What Risks Play a Role

The risk of thrombosis is not equally high for everyone. Various circumstances can promote the formation of a blood clot. People at increased risk of thrombosis include:

• those with limited mobility due to bed rest or long journeys
• after surgeries
• those who are overweight
• smokers
• those with cancer or undergoing cancer therapy
• those with congenital or acquired clotting disorders
• those experiencing hormonal changes due to pregnancy, hormonal contraceptives, or hormone replacement therapy
• those with inflammation
• those with cardiovascular diseases
• those with a history of previous thromboses
• those of increasing age (from about 40 years)⁴

Preventing Thrombosis

A healthy lifestyle plays a central role in preventing thrombosis. Regular exercise is particularly important as it promotes circulation and keeps the veins active. Even small changes in daily life can help: taking the stairs instead of the elevator, short walks instead of car rides, or using a bicycle instead of public transport. Sports such as hiking, cycling, swimming, or walking improve vein health and keep muscles active. For longer trips, experts also recommend compression stockings or even the temporary use of a blood thinner (e.g., heparin injected under the skin).

Proper nutrition and adequate fluid intake also support vascular health. A balanced, fiber-rich diet with plenty of fruits, vegetables, whole grains, and plant-based fats can have a positive effect. Equally important is sufficient hydration. About two liters of fluid daily help keep the blood thin.

Unnecessary risk factors such as smoking or being overweight should be avoided. People who have already had a thrombosis should be particularly cautious, as their risk of recurrence is increased.