CT Angiography May Not Be Needed for Suspected Pulmonary Embolism

Laurie Barclay, MD

June 15, 2010

June 15, 2010 — Computed tomography (CT) angiography may not be needed to rule out suspected pulmonary embolism (PE) in patients who have no risk factors, according to the results of a study reported online June 15 and in the August print issue of Radiology.

"Our study suggests that the frequency of ordering CT angiograms can be markedly reduced with resultant cost-savings and decreased radiation exposure," said lead author Mark D. Mamlouk, MD, radiology resident at the University of California, Irvine in Orange, California, in a news release.

"Thromboembolic risk factor assessment is an effective clinical method to determine when to perform CT angiography for PE," Dr. Mamlouk said. "Risk assessment can be performed when clinicians acquire their patients' history. It takes only a few minutes, and there's no cost."

The goal of the study was to evaluate the efficacy of thromboembolic risk factor assessment in accurately determining pretest probability for PE. The investigators retrospectively reviewed electronic medical records of 2003 patients who had CT angiography to detect possible PE from July 2004 to February 2006. Data were collected on thromboembolic risk factors including age, sex, immobilization, malignant disease, hypercoagulable state, excess estrogen state, and history of venous thromboembolism. The researchers determined the significance of each risk factor using logistic regressions.

Of 2003 patients, 1806 (90.16%), had CT angiogram results negative for PE, and 197 (9.84%) had CT angiogram results positive for PE. Of the group with positive results, 6.36% were seen in the emergency department, and 13.46% were inpatients.

One or more risk factors for PE was present in 192 (97.46%) of the 197 patients with CT angiogram results positive for PE. The most common risk factor for PE in this group was age 65 years or older, which was present in 69.04%. Risk factors were absent in 520 (28.79%) of the 1806 patients with CT angiogram results negative for PE.

Among all patients, the sensitivity of risk factor assessment was 97.46%, and the negative predictive value was 99.05%. The likelihood of having a positive result on CT angiogram for PE was even lower in patients with no risk factors and a negative D-dimer result. Multivariate logistic regression showed that all risk factors, except sex, were significant (P < .031).

Limitations of this study include retrospective design, review of CT angiography reports rather than images, relatively low number of D-dimer studies, and the subjective analysis of immobilization.

"In the setting of no risk factors, it is extraordinarily unlikely (0.95% chance) to have a CT angiogram positive for PE," the study authors write. "This selectivity and triage step should help reduce current costs and radiation exposure to patients."

The study authors have disclosed no relevant financial relationships.

Radiology. Published online June 15, 2010.