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Risk factors
By Mayo Clinic staff
Although anyone can develop blood clots and subsequent pulmonary embolism, certain factors can increase your risk.
Prolonged immobility
Blood clots are more likely to form in your legs during periods of inactivity, such as:
- Bed rest. Being confined to bed for an extended period after surgery, a heart attack, leg fracture or any serious illness makes you far more vulnerable to blood clots.
- Long journeys. Sitting in a cramped position during lengthy plane or car trips slows the current of blood flow, which contributes to the formation of clots in your legs.
Age
Older people are at higher risk of developing clots. Factors include:
- Valve malfunction. Tiny valves within your veins keep your blood moving in the right direction. These valves tend to degrade with age. When they don't work properly, blood pools and sometimes forms clots.
- Dehydration. Older people are at higher risk of dehydration, which may thicken the blood and make clots more likely.
- Medical problems. Older people are also more likely to have medical problems that expose them to independent risk factors for clots — such as joint replacement surgery, cancer or heart disease.
Family history
You're at higher risk of experiencing future clots if you or any of your family members have had blood clots or pulmonary embolism in the past. This may be due to inherited disorders of clotting that can be measured in specialty labs.
Surgery
Surgery is one of the leading causes of problem blood clots, especially joint replacements of the hip and knee. During the preparation of the bones for the artificial joints, tissue debris may enter the bloodstream and help cause a clot. Simply being immobile during any type of surgery can lead to the formation of clots. The risk increases with the length of time you are under general anesthesia.
Medical conditions
- Heart disease. High blood pressure and cardiovascular disease make clot formation more likely.
- Pregnancy. The weight of the baby pressing on veins in the pelvis can slow blood return from the legs. Clots are more likely to form when blood slows or pools.
- Cancer. Certain cancers — especially pancreatic, ovarian and lung cancers — can increase levels of substances that help blood clot, and chemotherapy further increases the risk. Women with a history of breast cancer who are taking tamoxifen or raloxifene also are at higher risk of blood clots.
Lifestyle
- Smoking. For reasons that aren't well understood, tobacco use predisposes some people to blood clot formation, especially when combined with other risk factors.
- Being overweight. Excess weight increases the risk of blood clots — particularly in women who smoke or have high blood pressure.
- Supplemental estrogen. The estrogen in birth control pills and in hormone replacement therapy can increase clotting factors in your blood, especially if you smoke or are overweight.
- Pulmonary embolism. National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/pe/pe_what.html. Accessed June 26, 2009.
- Thompson BT, et al. Overview of acute pulmonary embolism. http://www.uptodate.com/home/index.html. Accessed June 26, 2009.
- Kline JA, et al. Pulmonary embolism and deep venous thrombosis. In: Marx JA, et al. Rosen's Emergency Medicine: Concepts and Clinical Practices. 6th ed. Philadelphia, Pa.: Mosby Elsevier; 2006. http://www.mdconsult.com/das/book/body/146574529-3/0/1365/250.html#4-u1.0-B0-323-02845-4..50092-5--cesec18_4265. Accessed June 29, 2009.
- Bauer KA, et al. Overview of causes of venous thrombosis. http://www.uptodate.com/home/index.html. Accessed June 26, 2009.
- Deep vein thrombosis. American Academy of Orthopaedic Surgeons. http://orthoinfo.aaos.org/topic.cfm?topic=A00219. Accessed June 29, 2009.
- Tapson VF. Pulmonary embolism. In: Goldman L. Cecil Medicine. 23rd ed. Philadelphia, Pa.: Saunders Elsevier; 2007. http://www.mdconsult.com/das/book/body/146574529-5/0/1492/393.html#4-u1.0-B978-1-4160-2805-5..50104-X--cesec7_4150. Accessed June 29, 2009.
- Pulmonary hypertension. National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/pah/pah_what.html. Accessed June 29, 2009.
- Ferri FF. Pulmonary embolism. In: Ferri FF. Ferri's Clinical Advisor 2009. Philadelphia, Pa.: Mosby Elsevier; 2009. http://www.mdconsult.com/das/book/body/146779547-3/0/1701/492.html#4-u1.0-B978-0-323-04134-8..50019-7--subchapter69_10424. Accessed June 30, 2009.
- General nuclear medicine. Radiological Society of North America. http://www.radiologyinfo.org/en/info.cfm?PG=gennuclear. Accessed June 30, 2009.
- Catheter angiography. Radiological Society of North America. http://www.radiologyinfo.org/en/info.cfm?PG=Angiocath. Accessed June 30, 2009.
- Lip GY, et al. Patient information: Deep vein thrombosis (DVT). http://www.uptodate.com/home/index.html. Accessed June 30, 2009.
- Deep vein thrombosis. National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/Dvt/DVT_All.html. Accessed June 30, 2009.
- Rosenow EC (expert opinion). Mayo Clinic, Rochester, Minn. July 5, 2009.
