Pulmonary Embolism (cont.)
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. Looking at the list of deep vein thrombosis risk factors, one can
imagine that a d-Dimer blood test may not be helpful in those with significant
risk factors for deep vein thrombosis.
CT scan
If there is greater suspicion, then
computerized tomography (CT
scan) of the chest with
angiography can be done. Contrast 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. There are risks with this test since some
patients are allergic to the dye, and the contrast dye 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.
Next: Venous Doppler study »
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