Blood clots


Blood clots are clumps that occur when blood hardens from a liquid to a solid.

  • A blood clot that forms inside one of your veins or arteries is called a thrombus. A thrombus may also form in your heart.
  • A thrombus that breaks loose and travels from one location in the body to another is called an embolus.

A thrombus or embolus can partly or completely block the flow of blood in a blood vessel.

  • A blockage in an artery may prevent oxygen from reaching the tissues in that area. This is called ischemia. If ischemia is not treated promptly, it can lead to tissue damage or death.
  • A blockage in the vein will often cause fluid buildup and swelling.

Alternative Names

Clot; Emboli; Thrombi; Hypercoagulable state


Situations in which a blood clot is more likely to form in veins include:

  • Being on long-term bed rest
  • Crossing your legs for long periods when sitting, or sitting for long periods, such as in a plane or car
  • During and after pregnancy
  • Taking birth control pills or estrogen hormones (especially in women who smoke)
  • Long-term use of an intravenous catheter
  • After surgery

Blood clots are also more likely to form after an injury. People with cancer, obesity, and liver or kidney disease are also prone to blood clots.

A buildup of cholesterol that narrows an artery may change or slow the flow of blood, making it easier for a blood clot or thrombus to form.

Conditions that are passed down through families (inherited) may make you more likely to form abnormal blood clots. Inherited conditions that affect clotting are:

A blood clot may block an artery or vein in the heart, affecting the:


Schafer AI. Thrombotic disorders: hypercoagulable states. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 176.

Review Date: 5/20/2016
Reviewed By: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
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