What is Thrombosis?

Thrombosis is the process of a blood clot, also known as a thrombus, forming in a blood vessel. This clot can block or obstruct blood flow in the affected area, as well as cause serious complications if the clot moves to a crucial part of the circulatory system, such as the brain or the lungs.

It is normal for the body to produce clotting factors like platelets and fibrin when a blood vessel is injured, to prevent an excessive loss of blood from the body. If this effect is over productive it can obstruct the flow of blood and form an embolus that moves around the blood stream.

Thrombosis Types

Thrombosis can be broadly classified as either venous thrombosis or arterial thrombosis, according to where the thrombus presents in the body.

Venous thrombosis occurs in the veins and is categorized further according to where it occurs including:

  • Deep vein thrombosis
  • Portal vein thrombosis
  • Renal vein thrombosis
  • Jugular vein thrombosis
  • Budd-Chiari Syndrome
  • Paget-Schoetter disease
  • Cerebral venous sinus thrombosis

Arterial thrombosis, also known as atherothrombosis due to its association with atheroma rupture, occurs in the arteries. The blood stasis caused by atrial fibrillation may also cause this type of thrombosis.

There are multiple causes for stroke, including ischemia, hemorrhage and embolus in the brain. Stroke due to a blood clot in the brain usually builds gradually around an atherosclerotic plaque.

Myocardial infarction may also be caused by a thrombus in the coronary artery and is associated with ischemia. The reduced oxygen supply to the heart cells, as a result of the blockage, results in cell death and myocardial infarction.


There are three main causes of thrombosis: hypercoagulability, injury to the endothelial cells of the blood vessel wall and abnormal flow of the blood.

Hypercoagulability, also known as thrombophilia, refers higher levels of coagulation factors in the blood that increase susceptibility to thrombosis. This is usually as a result of genetics or disorders of the immune system.

Injury to the epithelial cells on the wall of blood vessels after trauma, surgery or and infection can also precipitate coagulation and possible thrombosis.

Abnormal blood flow, such as venous stasis following heart failure or long periods of sedentary behavior, can also cause thrombosis to occur. Additionally, some other health conditions can affect blood flow and lead to the production of a thrombus, including atrial fibrillation and cancer.


A common complication of thrombosis is hypoxia, due to the obstruction of the artery of vein. When the majority of the blood vessel is blocked, the oxygen supply to the body is reduced and results in increased production of lactic acid.

Additionally, in some cases the blood clot may break free and travel around the body, a process known as embolization. This can obstruct the blood flow to essential organs, such as the brain or the lungs, reducing or inhibiting oxygen and blood flow with severe repercussions.

Prevention and Treatment

As stasis of the blood is associated with increased risk of thrombosis, it is important that movements are made regularly, particularly if susceptible individuals are likely to be sedentary for long periods of time, such as in bed or on an airplane.

For people at high risk of venous thromboembolism, heparin can be administered to reduce risk of pulmonary embolism, although this is associated with higher susceptibility to bleeding due to the reduced efficacy of the clotting factors. Therefore, heparin offers greater use in the treatment, rather than prevention of thrombosis.

A more coherent method to prevent the formation of deep vein thrombosis is the use of compression stockings, which mechanically support the vein to inhibit the formation of blood clots. This is particularly beneficial as there are few side effects.

Anticoagulants may increase the risk of major bleeding slightly, but has been found to offer a benefit in both the prevention and treatment of thrombosis.


Further Reading

Last Updated: Aug 23, 2018

Yolanda Smith

Written by

Yolanda Smith

Yolanda graduated with a Bachelor of Pharmacy at the University of South Australia and has experience working in both Australia and Italy. She is passionate about how medicine, diet and lifestyle affect our health and enjoys helping people understand this. In her spare time she loves to explore the world and learn about new cultures and languages.


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  1. Birgir Norddahl Birgir Norddahl United States says:

    Denne artikl skal redigeres. Den er formodenligt skrevet med en "Google-oversaettelse" fra en engelsk artikel.
    This article needs revision. It is written presumably from an English article with Google Translate.

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