Clinical study
The effect of helical computed tomography on diagnostic and treatment strategies in patients with suspected pulmonary embolism

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Abstract

Background

Helical computed tomography (CT) has been proposed as a first-line test for the diagnosis of pulmonary embolism. How the test affects the diagnostic evaluation of patients with suspected pulmonary embolism is unknown.

Methods

We examined a cohort of 360 patients evaluated for pulmonary embolism at a teaching hospital in the 4 years following the introduction of the helical CT scan. We collected patient demographic and clinical data to calculate the pretest likelihood of pulmonary embolism; we then read the test results and determined rates of further testing and treatment for pulmonary embolism.

Results

After the helical CT scan became available, the number of patients referred for pulmonary embolism testing increased markedly from 170 to 624 total evaluations during 1997 to 2000 (P <0.01). This rise was due to increased use of the helical CT scan (9% to 83% of evaluations, P <0.01) as the use of ventilation-perfusion scanning (79% to 17%, P = 0.03) and pulmonary angiography (12% to <1%, P <0.01) fell. There was no change in the pre-test likelihood of disease over time, but the percentage of scans that were positive for pulmonary embolism rose (14% to 32%, P =0.02). Clinicians treated all patients who had a positive CT scan, but became less likely over time to order further testing for patients who had a negative scan (30% to 12%, P = 0.02).

Conclusion

At this academic medical center, introduction of the helical CT scan had a profound effect on the evaluation of pulmonary embolism, resulting in more frequent use of the CT scan, and more frequent diagnosis and treatment of pulmonary embolism, despite no change in the pretest probability of disease. Future studies should confirm our findings and determine whether increased detection of pulmonary emboli results in improved outcomes.

Section snippets

Study design and sample

We performed a retrospective investigation of patients referred for radiographic evaluation of pulmonary embolism over a 4-year period (1997 to 2000) at Moffitt-Long Hospital, a 535-bed academic medical center affiliated with the University of California, San Francisco. In 1997, the Department of Radiology at the hospital began to offer helical CT scanning for the diagnosis of pulmonary embolism. Throughout the study period, CT scans were available 24 hours a day; all scans were read by a core

Results

A total of 410 charts were identified and reviewed to reach our goal of 360 charts. Of the 50 charts excluded, 25 (6%) were baseline or follow-up examinations without clinical suspicion for acute pulmonary embolism, 23 (6%) were incomplete, and 2 (<1%) pertained to tests that were not the initial investigation for pulmonary embolism. There were no statistical differences in the number of charts excluded or reasons for exclusion across study periods. Results of blinded rereading of initial CT

Discussion

In our study, introduction of the helical CT scan had a profound effect on diagnostic strategies and test utilization in patients with suspected pulmonary embolism. The helical CT scan almost completely replaced the ventilation-perfusion scan as the first-line test and led to a substantial increase in the total number of evaluations for pulmonary embolism. This shift occurred without any change in the likelihood of pulmonary embolism among patients referred for testing and may have resulted in

Acknowledgements

The authors gratefully acknowledge Erin Hartman for editorial assistance in the preparation of this manuscript, and Alan Bostrom, PhD, for his statistical expertise.

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