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Helical Computed Tomography for Diagnosing Pulmonary Embolism
- Suman W. Rathbun, MD;
- Gary E. Raskob, PhD; and
- Thomas L. Whitsett, MD
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IN RESPONSE:
We stand by the conclusions of our systematic review: 1) The use of helical CT in the diagnosis of pulmonary embolism has not been adequately evaluated; 2) the safety of withholding anticoagulant treatment in patients with negative results on helical CT is uncertain; and 3) definitive large, prospective studies should be done to evaluate the sensitivity, specificity, and safety of helical CT for diagnosis of suspected pulmonary embolism. These conclusions are appropriate on the basis of the available evidence from studies in patients.
The data quoted by Mayo and colleagues are from a study performed in animals (1). Such data are not sufficient for making recommendations about the care of patients. These data do, however, provide two interesting observations. First, the sensitivity of helical CT for pulmonary embolism in this animal model was 82%. This sensitivity is not sufficiently high to support the use of helical CT for excluding the presence of pulmonary embolism. Second, the observed sensitivity for angiography (only 87%) challenges the clinical relevance of this experimental model. Pulmonary angiography has been shown to be a valid gold standard in patients with suspected pulmonary embolism (2). The follow-up of more than 600 consecutive patients with negative pulmonary angiograms in the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study documented a very low incidence of symptomatic venous thromboembolism (0.6% [4 of 675 patients]) (2). These data establish pulmonary angiography as a valid gold standard for pulmonary embolism. A prospective study comparing helical CT with pulmonary angiography is both feasible and clinically relevant. Alternately, a prospective study to document clinical outcome on follow-up of patients with negative helical CT results in whom anticoagulant therapy is withheld without additional testing for venous thromboembolism would provide clinically useful information. Such a study is also feasible and has been used to validate the negative results of objective tests for pulmonary embolism, including pulmonary angiography (2) and perfusion lung scanning (3).
On the basis of the available evidence from studies in patients, the role of helical CT in the diagnosis of suspected pulmonary embolism remains uncertain because of the unknown validity of a negative result and the lack of data from definitive prospective studies on which to base a rigorous cost-effectiveness analysis. Our conclusions are supported by an independent systematic review that reached almost identical conclusions (4).
Suman W. Rathbun, MD
Gary E. Raskob, PhD
Thomas L. Whitsett, MD
University of Oklahoma Health Sciences Center; Oklahoma City, OK 73190
The Editors welcome submissions for possible publication in the Letters section. Authors of letters should:
•Include no more than 300 words of text, three authors, and five references
•Type with double-spacing
•Send three copies of the letter, an authors' form signed by all authors, and a cover letter describing any conflicts of interest related to the contents of the letter.
Letters commenting on an Annals article will be considered if they are received within 6 weeks of the time the article was published. Only some of the letters received can be published. Published letters are edited and may be shortened; tables and figures are included only selectively. Authors will be notified that the letter has been received. If the letter is selected for publication, the author will be notified about 3 weeks before the publication date. Unpublished letters cannot be returned.
Annals welcomes electronically submitted letters.
- Copyright ©2004 by the American College of Physicians
