Pulmonary embolism, or PE, is a potentially fatal condition in which an artery supplying blood to the lungs suffers a blockage caused by a blood clot, or thrombus. While the classic signs of pulmonary embolism, such as sudden chest pain, lack of oxygen and inability to breathe, may make diagnosis easier, often pulmonary embolism diagnosis can be difficult because the condition presents itself in a nonspecific way, with symptoms which are not obvious. If embolism is suspected, tests are used to exclude other conditions as well as to confirm PE, and may include chest X-rays, lung ventilation scans, ultrasound and CT scans. A D-dimer test can detect the presence of blood clots in the circulation, and an angiogram gives an image of blood flow through the lungs.
Venous thromboembolism is the term used to describe the processes which most often lead to blood clots lodging in the lungs. Most often, clots travel in the bloodstream from the deep veins in the legs, where they will have formed due to a condition known as deep venous thrombosis. Deep venous thrombosis tends to occur when people are inactive for a prolonged period, perhaps due to bed rest or a long journey by air. As people in the hospital are often confined to bed, the condition is common in a hospital setting and, if a piece of clot breaks off and travels to block a lung artery, pulmonary embolism may occur and breathing may become difficult. Timely treatment with drugs which prevent clotting and dissolve existing clots is necessary to preserve life.
Pulmonary embolism diagnosis usually begins with the use of clinical scoring systems before any tests are carried out. These systems look at clinical findings such as the symptoms, signs and history of the patient and use these to assess the probability that the patient has a pulmonary embolism. Establishing whether the probability is high or low can determine which tests are carried out next.
Chest X-rays help to exclude other conditions which might cause chest pain, although they cannot be used to confirm a pulmonary embolism diagnosis. The D-dimer blood test is used in cases where the probability of a pulmonary embolism is low, because a negative result then tends to rule out PE. In patients who are unlikely to have another lung disease, measuring arterial blood gases can help to make a pulmonary embolism diagnosis. If the oxygen level is low, PE is more likely.
CT scans, which can create three-dimensional X-ray images, may be used to make a pulmonary embolism diagnosis. If CT technology is not available, a lung ventilation scan can provide images of air movement and blood flow in the lungs, giving useful diagnostic information. A pulmonary angiogram involves injecting dye into the arteries of the lungs to display an outline of the arterial network on an X-ray image. This test is an accurate method of establishing a pulmonary embolism diagnosis, but as it is difficult to perform it is used when other, simpler tests have failed to give a definite answer.