Synonyms: Blood clot, Venous thrombosis

Medical Specialties: Cardiology, Emergency medicine, Internal medicine

Clinical Definition

Thrombosis is the formation of a thrombus (blood clot). Thrombosis may occur in a blood vessel or in a chamber of the heart. A thrombus may block blood flow, either partly or completely, through the blood vessel. If a thrombus develops in a vein deep in the body, it is known as a deep vein thrombosis (DVT) or venous thrombosis. If a thrombus travels to the lungs, it is known as a pulmonary embolism.

In Our Own Words

Thrombosis refers to the formation of a blood clot (thrombus) either in a blood vessel or in one of the heart's chambers. Often, this clot will develop in a vein deep in the body, called deep vein thrombosis, or DVT. Normally these clots occur in the lower leg, the thigh or the pelvic area, but can occur in other parts of the body as well. 


When a thrombus breaks free and travels, it may cause a thromboembolism, which can be dangerous and life-threatening. It can journey to the lungs and lodge there, becoming a pulmonary embolism. DVT can result in complications in the leg, including chronic venous insufficiency or post-thrombotic syndrome. The affected leg can also experience pressure, chronic swelling or even ulcers. This can be a serious medical emergency. 

Relevant Conditions
Common Types
  • DVT
  • Arterial thrombosis
  • Venous thrombosis
Side Effects
  • Swelling or pain in an extremity
  • Feeling of warmth in swollen extremity
  • Skin redness
Share this article
  • Harvard Medical School. "Medical Dictionary of Health Terms." Harvard Health Publications. 2013. Accessed Aug. 2013.
  • Center for Disease Control and Prevention. "DVT Facts." Sept. 2012. Accessed Aug. 2013.
  • The Cleveland Clinic. "Deep Vein Thrombosis." Diseases & Conditions. June 2011. Accessed Aug. 2013.
  • The Cleveland Clinic. "Thrombosis Center." Blood clotting disorders 2013. Accessed Aug. 2013.
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