Blood clots form when the blood coagulates from a liquid to a solid. Normally, clots form in response to a cut or other injury, stopping the bleeding from an artery or vein. Sometimes, however, a clot forms for other reasons, blocking the flow of blood and oxygen, to that area. If the clot forms inside a blood vessel and stays there, it is called a thrombus.
A clot in a deep vein, called deep vein thrombosis or DVT, can break off and travel to another part of the body, causing a stroke, heart attack or pulmonary embolism. Approximately 350,000 to 600,000 people in the United States have a deep vein thrombosis, also called DVT, or a pulmonary embolism every year, and at least 100,000 die, according to the Centers for Disease Control and Prevention.
Blood clots in the leg usually form for one of several reasons: inactivity, trauma to the vein, hypercoagulability of the blood or chronic disease. Risk factors include age, obesity, family history and previous blood clots.
Injury
Fractures, severe muscle injury and major surgery involving the abdomen, pelvis, hip or legs can damage the inner lining of the vein, causing it to form a blood clot. Inflammation and an immune response can have the same effect.
Inactivity
Immobility can cause sluggish or slow blood flow. Nearly half of all DVT cases are caused by inactivity, including hospitalization, long travel, confinement to bed or limited movement due to a cast or paralysis.
Hypercoagulation
Certain conditions and medications can make the blood thicker or more likely to clot than normal. Hormone replacement therapy, birth control pills, inherited blood clotting disorders and pregnancy up to six weeks after delivery can cause hypercoagulation. Certain diseases, such as heart disease, cancer, lung disease and inflammatory bowel disease, can also cause hypercoagulation.
