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A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M.; 2013.
A.D.A.M. Medical Encyclopedia.
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, incidence, and risk factors
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:
- Heart (angina or a heart attack)
- Intestines (mesenteric ischemia) or mesenteric venous thrombosis
- Kidneys (renal vein thrombosis)
- Legs (deep vein thrombosis)
- Lungs (pulmonary embolism)
- Neck or brain (stroke)
References
- Schafer AI. Thrombotic disorders: hypercoagulable states. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 179.
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.
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Screening people aged over 65 years for atrial fibrillation increases the rate of detection
Atrial fibrillation is a common cardiac arrhythmia that makes the heart beat rapidly and irregularly. This can occur for brief episodes or may be continuous. Symptoms of the disease include heart palpitations, chest pain, shortness of breath, light‐headedness and fatigue. The condition is rare in those under 40 years but gets more common as people age. Not everyone with atrial fibrillation experiences symptoms so some people are unaware that they have it, while others may experience mild symptoms that they do not attribute to the disease. Atrial fibrillation hinders the efficient flow of blood through the heart, resulting in an increased risk of clot formation. If these clots leave the heart they can block the vessels supplying blood to the brain, causing a stroke. Treatment with anticoagulant medication is designed to prevent the formation of blood clots and can reduce the risk of stroke by over 60%.
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