Chest CTA combined with leg CT boosts pulmonary embolism detection

Combining a CT scan of the legs with chest CT angiography increases the chances of detecting pulmonary embolism, according to a multicenter study funded by the National Heart, Lung, and Blood Institute.

Pulmonary embolism leads to death in nearly one-third of untreated cases, but therapies lower the death rate to between 3% and 8%. In nine out of 10 cases, PE begins as a clot that breaks free from the deep veins of the leg.

Physicians should consider additional test results before ruling out PE in patients whose CTA scan does not detect clots but whose clinical assessment suggests a high likelihood of PE, the study said.

The study, published in the June 1 issue of The New England Journal of Medicine, is part of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) II trial. PIOPED is the largest study ever conducted to assess the role of contrast-enhanced multislice CTA for diagnosing PE.

Researchers from eight clinical centers compared the accuracy of three ways to diagnose blood clots in 824 patients suspected of having PE: chest CTA alone, chest CTA with venous-phase imaging (leg CT), and chest CTA with an objective clinical assessment known as the Wells Score.

They reported that chest CTA alone detected suspected PE in only 83% of patients compared with 90% for the combined results of chest CTA and leg CT. The specificity was similar (95%) for chest CT alone and the combined chest and leg CT.

A high clinical probability combined with positive chest CTA correctly indicated PE in 96% of participants. In patients with a high clinical probability, however, a negative chest CT result did not confidently rule out a diagnosis of PE, according to the study.

Chest CTA is good but sometimes not enough, said lead author Dr. Paul D. Stein, a professor of medicine at Wayne State University who chaired the PIOPED II steering committee.

The results of the chest CT combined with the patient's clinical probability assessment were comparable to the results from the combined chest CT and leg CT scans.

"Our study spells out the strengths and weaknesses of chest CTs for diagnosing pulmonary embolism, and it will help guide physicians on when more tests are needed," Stein said.

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