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Diagnosis of Pulmonary Embolism Reviewed and Updated
Henry I. Bussey, Pharm.D.
Reference: Clemens S, Leeper KV Jr. Newer modalities for detection of pulmonary emboli. Am J Med. 2007 Oct;120(10 Suppl 2):S2-12.
The authors of this review discuss the advances that have been made over the past 10 years in identifying the best ways to diagnose pulmonary embolism. Because untreated pulmonary embolism (PE) can be fatal, and because anticoagulation therapy can be dangerous, it is important to employ a diagnostic approach that will be both sensitive and specific, respectively. The exact type of test, however, also may depend on what is readily available in a given institution. Patient safety and cost-effectiveness also should be considered in selecting the most appropriate test(s). The authors provide extensive detail on the sensitivity, specificity, and safety of the various available tests – including, for example, the various types of d-Dimer tests that are available and the various types of ventilation/perfusion tests that are available. The following observations, therefore, should be viewed as generalizations and the reader is encouraged to review the actual manuscript for detailed discussions of the advantages and disadvantages of the different types of tests that are currently available.
When the risk or likelihood of the patient actually having a PE is low or intermediate, the authors indicate that a negative (or normal) d-Dimer test is adequate to rule out PE. According to the authors, about one-third of suspected PE patients may require only the d-Dimer test. If the d-Dimer test is abnormal (elevated) or the clinical probability of a PE is high, additional testing is recommended. For most patients the authors recommend a computer tomography test of the chest (peferrably a multidetector spiral computed tomography or MDCT) and CT angiography of the lower extremities. The CT angiography of the lower extremities is recommended because of the risk of a false negative MDCT result. The chest CT is very specific for PE if positive, but a false negative chest CT could lead to inappropriate withholding of therapy for such a patient. Therefore, the scan of the legs is recommended as a method to reduce the likelihood of a false-negative diagnosis based solely on a false-negative chest CT. Although the authors recommend a CT angiography of the lower extremities, compression ultrasonography of the lower extremities is a reasonable alternative. For patients at high risk of test toxicity (such as pregnant women, nursing mothers, and/or those with renal insufficiency), the authors recommend the traditional ventilation/perfusion (V/Q) test as the safest test for those patient sub-groups. A normal or low-probability V/Q scan result is quite effective at ruling out PE.
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