Venous thromboembolism is a blood clot formed in a vein and can travel in the network of blood vessels until it blocks a blood vessel. Deep vein thrombosis occurs when a blood clot blocks a vein, typically in the leg. Pulmonary embolism occurs when a blood clot travels to the lungs and blocks the blood supply to a part of the lungs.
Blood clots can be triggered by medical procedures or by other medical conditions, or by periods of immobilization such as lying in a hospital bed or a long flight. Blood can also clot easier in certain medical conditions such as cancer and autoimmune disorders, with medical treatments, with hormone therapy, due to inherited conditions, and with increasing age.