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Blood clots
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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.

2. 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:
Heart (angina or a heart attack)
Intestines (mesenteric ischemia) or mesenteric venous thrombosis
Kidneys (renal vein thrombosis)
Leg or arm arteries
Legs (deep vein thrombosis)
Lungs (pulmonary embolism)
Neck or brain (stroke)
Alternative Names
Clot; Emboli; Thrombi; Hypercoagulable state
References
Schafer AI. Thrombotic disorders: hypercoagulable states. In: Goldman L, Schafer
AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 179.
Update Date: 6/5/2012

3. Updated 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.
Browse the Encyclopedia
MedlinePlus Topics
Blood Clots
Images
Thrombus
Janeway lesion on the finger
Deep venous thrombosis, ileofemoral
Read More
Angina
Arterial embolism
Atheroembolic renal disease
Deep venous thrombosis
Hardening of the arteries
Heart attack
Limb plethysmography
Necrosis
Pulmonary embolus
Renal vein thrombosis
Stroke
Thrombophlebitis
Venogram
Patient Instructions
Deep vein thrombosis - discharge
Taking warfarin (Coumadin)
Taking warfarin (Coumadin) - what to ask your doctor

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