Blood clots

Definition

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 usually cause fluid buildup and swelling.

Causes

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

Being on long-term bed rest

Crossing your legs for long periods of time when sitting, or sitting for long periods of time, such as in a plane or car

During and after pregnancy

Not having enough water in your body (dehydration)

Taking birth control pills or estrogen hormones (especially in women who smoke)

Using an intravenous catheter long-term

Blood clots are also more likely in people with cancer, recent surgery or injury, obesity, and liver or kidney disease.

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:

Factor V Leiden thrombophilia

Prothrombin G20210A mutation

Other rare conditions such as protein C, protein S, and antithrombin III deficiencies

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

Review Date: 6/5/2012
Reviewed By: Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington; and Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.

This information should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. © 1997- 2007 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.