Negative CT scan rules out pulmonary embolism

A report in the Journal of the American Medical Association recommends CT scanning over pulmonary angiography as the preferred way to rule out pulmonary embolism.

Using on a meta-analysis of peer-reviewed medical literature, researchers at Brigham and Women's Hospital, Harvard Medical School, and the Medical University of South Carolina reported that single-slice CT is as accurate as conventional pulmonary angiography for excluding PE.

The study appeared in the April 27 issue of JAMA.

While CT is seeing increasing use for this application, studies and papers continue to compare the accuracy of CT exams with pulmonary angiography, said coauthor Dr. U. Joseph Schoepf, an associate professor of radiology at the Medical University of South Carolina.

"These studies ought to be obsolete. We have shown convincingly that CT is the new gold standard with its high negative predictive value," he said.

Schoepf and colleagues analyzed the frequency of venous thromboembolic events, deaths attributed to PE, and false negative reports on a total of 3500 patients included in selected studies from 1994 through 2002.

A chest CT scan negative for PE indicates an overall negative likelihood ratio for a venous thromboembolic event of 0.07 and a negative predictive value of 99.1%, the researchers said. This high NPV compares favorably with values for pulmonary angiography, according to the study authors.

The overall negative likelihood ratio for mortality attributable to PE was 0.01, with an overall NPV of 99.4%.

The researchers found no significant difference in the risk of a venous thromboembolic event between single-slice and multislice CT, although only about 200 cases out of the 3500 were done using MSCT.

The negative predictive value for ruling out pulmonary embolism for even single-slice CT was similar to that for pulmonary angiography, so the values should be even better for MSCT, Schoepf said.

CT's alleged insensitivity for isolated peripheral pulmonary embolisms fuels continuing debate over which is the better test in this application, according to Schoepf.

"We know from previous studies that variable interobserver results make pulmonary angiography not a very reliable test. You artificially degrade the value of CT by comparing it to pulmonary angiography as a gold standard. Based on our results, I would advise against such further studies," he said.

The meta-analysis was based on a review of medical literature identified using PubMed, MEDLINE, EMBASE, CRISP, metaRegister of Controlled Trials, and Cochrane.

For more information from the online Diagnostic Imaging archives:

Multislice CT emerges as gold standard for chest imaging

MSCT tackles acute chest pain in emergency room