Blood clots naturally to stop bleeding after an injury. However, sometimes blood clots form when no injury has occurred; when this happens, blood flow through an artery or vein can be impeded, leading to varicose veins or serious, life-threatening afflictions like heart attack or stroke.
Injury, Illness or Surgery
Anyone who has had recent surgery is more likely to get a blood clot. Broken bones---such as in the leg, pelvis or hip---also increase risk of blood clots. Someone who has, or is being treated for, cancer also is at higher risk for developing clots.
Being Sedentary
Blood clots are more likely to occur when you stay in one place for an extended period of time, so blood clots are more common among those confined to bed or in a wheel chair. Trips in the car or by train or boat that require a person to stay stationary for more than an hour can lead to blood clots, too, particularly among those who are prone to getting them.
History
Those with a family history of blood clots---and anyone who has had a blood clot in the past---is more likely to get them. The risk also increases among those with heart problems, previous stroke or paralyzation, or tendency to develop varicose veins or other vascular conditions.
Other Possible Triggers
Blood clots are more common among those who are overweight, have inflammatory bowel disease or use birth control patches and pills. Women who are pregnant or recently gave birth---particularly by c-section---are at elevated risk for developing blood clots.
Less Common Causes
Blood clots also can occur when a catheter is inserted into a vein in the arm, pacemaker or implantable cardioverter defibrillator has been placed in the body, or cancer has appeared near a vein. In rare cases, blood clots also can result from repetitious arm activities.
