Almost 2 out of every 100 cases are fatal. Most cases come from blood clots in the veins of the leg. If the clot becomes loose, it can travel through the blood stream until it is stuck in a small vessel. Rarely, the lump, or embolus, is made up of fat, tumor cells, or other foreign items. Blood clots in the lungs are often caused by clots from veins in the legs.
Many cases are among persons already hospitalized for other reasons.
A person is more likely to have clots after surgery, stroke, long term bed rest or inactivity, or fractures of the hip or legs. There is a somewhat higher risk among overweight people and during pregnancy. If a clot lodges in the lungs, there may be sudden shortness of breath, chest pain, coughing up blood, and a low fever. The patient sometimes tightens chest muscles to avoid pain and may have swollen legs. A person with a large clot may pass out, appear bluish in color, and have bulging neck veins.