Many things increase your risk for a blood clot. These include:
- Having slowed blood flow, abnormal clotting, and a blood vessel injury.
- Age. As people get older (especially older than age 70), they are more likely to develop blood clots.
- Weight. Being overweight increases the risk for developing clots.
- Not taking anticoagulant medicine as prescribed, unless your doctor tells you to stop taking it.
Slowed blood flow
When blood does not circulate normally, clots are more likely to develop. Reduced circulation may result from:
- Long-term bed rest, such as if you are confined to bed after an operation, injury, or serious illness.
- Traveling and sitting for a long time, especially when traveling long distances by airplane.
- Leg paralysis. When you use your muscles, the muscles contract, and that squeezes the blood vessels in and around the muscles. The squeezing helps the blood move back toward the heart. Paralysis can reduce circulation because the muscles can't contract.
Some people have blood that clots too easily or too quickly. People with this problem are more likely to form larger clots that can break loose and travel to the lungs. Conditions that may cause increased clotting include:
- Inherited factors. Some people have an inherited tendency to develop blood clots that can lead to pulmonary embolism.
- Family history of close relatives, such as a sibling, who has had deep vein thrombosis or pulmonary embolism.
- Cancer and its treatment.
- Blood vessel diseases, such as varicose veins, heart attack, heart failure, or a stroke.
- Pregnancy. A woman's risk for developing blood clots increases both during pregnancy and shortly after delivery.
- Using hormone therapy or birth control pills or patches.
Injury to the blood vessel wall
Blood is more likely to clot in veins and arteries shortly after they are injured. Injury to a vein can be caused by:
- Recent surgery that involved the legs, hips, belly, or brain.
- A tube (catheter) placed in a large vein of the body (central venous catheter).
- Damage from an injury, such as a broken hip, serious burn, or serious infection.