October 5, 2015
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Pulmonary Embolism (cont.)

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d-Dimer blood test

If the healthcare provider's suspicion for pulmonary embolism is low, a d-Dimer blood test can be used. The d-Dimer blood test measures one of the breakdown products of a blood clot. If this test is normal, then the likelihood of a pulmonary embolism is very low. Unfortunately, this test is not specific for blood clots in the lung. It can be positive for a variety of reasons including pregnancy, injury, recent surgery, or infection. D-dimer is not helpful if the potential risk for a blood clot is high.

CT scan

If there is greater suspicion, then computerized tomography (CT scan) of the chest with angiography can be done. Contrast material (dye) is injected into an intravenous line in the arm while the CT is being taken, and the pulmonary arteries can be visualized. There are some limitations of the test, especially if a pulmonary embolism involves the smaller arteries in the lung. However similar problems are seen with the more invasive pulmonary angiogram. As CT scan has become more and more sophisticated, not identifying significant emboli is unusual. It is very important that the contrast material used during the CT angiogram be timed appropriately so that the bolus of dye is not diluted as it travels through the lungs.

There are risks with this test since some patients are allergic to the contrast material, and the contrast material can be harsh on kidney function especially if the patient's kidney function (as measured by blood tests) is marginal. It may be wise to limit the patient's exposure to radiation, especially in pregnant patients. However, since pulmonary embolus can be fatal, even in pregnancy this test can be performed, preferably after the first trimester.

Ventilation-perfusion scans

Ventilation-perfusion scans (VQ scans) use labeled chemicals to identify inhaled air into the lungs and match it with blood flow in the arteries. If a mismatch occurs, meaning that there is lung tissue that has good air entry but no blood flow, it may be indicative of a pulmonary embolus. These tests are read by a radiologist as having a low, moderate, or high probability of having a pulmonary embolism. There are limitations to the test, since there may be a 5%-10% risk that a pulmonary embolism exists even with a low probability V/Q result.

Medically Reviewed by a Doctor on 2/27/2015

Source: MedicineNet.com

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