Background:
The limitations of the current diagnostic standard, ventilation-perfusion lung scanning, complicate the management of patients with suspected pulmonary embolism. We previously demonstrated that determining the pretest probability can assist with management and that the high negative predictive value of certain d-dimer assays may simplify the diagnostic process.
Objective:
To determine the safety of using a simple clinical model combined with d-dimer assay to manage patients presenting to the emergency department with suspected pulmonary embolism.
Design:
Prospective cohort study.
Setting:
Emergency departments at four tertiary care hospitals in Canada.
Patients:
930 consecutive patients with suspected pulmonary embolism.
Interventions:
Physicians first used a clinical model to determine patients' pretest probability of pulmonary embolism and then performed a d-dimer test. Patients with low pretest probability and a negative d-dimer result had no further tests and were considered to have a diagnosis of pulmonary embolism excluded. All other patients underwent ventilation-perfusion lung scanning. If the scan was nondiagnostic, bilateral deep venous ultrasonography was done. Whether further testing (by serial ultrasonography or angiography) was done depended on the patients' pretest probability and the lung scanning results.
Measurements:
Patients received a diagnosis of pulmonary embolism if they had a high-probability ventilation-perfusion scan, an abnormal result on ultrasonography or pulmonary angiography, or a venous thromboembolic event during follow-up. Patients for whom the diagnosis was considered excluded were followed up for 3 months for the development of thromboembolic events.
Results:
The pretest probability of pulmonary embolism was low, moderate, and high in 527, 339, and 64 patients (1.3%, 16.2%, and 37.5% had pulmonary embolism), respectively. Of 849 patients in whom a diagnosis of pulmonary-embolism had initially been excluded, 5 (0.6% [95% CI, 0.2% to 1.4%]) developed pulmonary embolism or deep venous thrombosis during follow-up. However, 4 of these patients had not undergone the proper diagnostic testing protocol. In 7 of the patients who received a diagnosis of pulmonary embolism, the physician had performed more diagnostic tests than were called for by the algorithm. In 759 of the 849 patients in whom pulmonary embolism was not found on initial evaluation, the diagnostic protocol was followed correctly. Only 1 (0.1% [CI, 0.0% to 0.7%]) of these 759 patients developed thromboembolic events during follow-up. Of the 437 patients with a negative d-dimer result and low clinical probability, only 1 developed pulmonary embolism during follow-up; thus, the negative predictive value for the combined strategy of using the clinical model with d-dimer testing in these patients was 99.5% (CI, 99.1% to 100%).
Conclusion:
Managing patients for suspected pulmonary embolism on the basis of pretest probability and d-dimer result is safe and decreases the need for diagnostic imaging.
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Author, Article, and Disclosure Information
From the University of Ottawa, Ottawa, and University of Western Ontario, London, Ontario; Dalhousie University, Halifax, Nova Scotia; and University of British Columbia Vancouver, British Columbia, Canada.
Grant Support: By a grant from the Heart and Stroke Foundation of Nova Scotia and Ontario grant NA 3304. Dr. Philip Wells is a recipient of a Canada Research Chair; Dr. Stiell is a recipient of a Distinguished Scientist Award from the Canadian Institute of Health Research; Dr. Anderson is a Research Scholar of Dalhousie University; and Dr. Kovacs is an Internal Scholar of the Department of Medicine, University of Western Ontario.
Corresponding Author: Philips P. Wells, MD, MSc, Suite 452, 737 Parkdale Avenue, Ottawa, Ontario K1Y 1J8, Canada.
Current Author Addresses: Drs. Wells and Forgie: Division of Hematology, The Ottawa Hospital, Civic Campus, Suite 452, 737 Parkdale Avenue, Ottawa, Ontario K1Y 1J8, Canada.
Dr. Anderson: Division of Hematology, Queen Elizabeth II Health Science Centre, Bethune Building, Room 432, Victoria General Hospital Site, 1278 Tower Road, Halifax, Nova Scotia B3H 2Y9, Canada.
Drs. Barnes and G. Kovacs: Division of Hematology, Queen Elizabeth II Health Science Centre, Bethune Building, Victoria General Hospital Site, 1278 Tower Road, Halifax, Nova Scotia B3H 2Y9, Canada.
Dr. Rodger: Division of Hematology, The Ottawa Hospital General Campus, 501 Smyth Road, Ottawa, Ontario K1H 8L6, Canada.
Dr. Dreyer: London Health Sciences Centre, Victoria Campus, Box 5375 Station B, London, Ontario N6A 4G5, Canada.
Dr. Stiell: Emergency Department, The Ottawa Hospital Civic Campus, 1053 Carling Avenue, Ottawa, Ontaio K1Y 4E9, Canada.
Dr. Ward: Emergency Department, St. Paul's Hospital, 1081 Burrand Street, Vancouver, British Columbia V6Z 1Y6, Canada.
Dr. M. Kovacs: Department of Hematology, University of Western Ontario, 800 Commisioners Road East, London, Ontario N6A 4G5, Canada.
Author Contributions: Conception and design: P.S. Wells, D.R. Anderson, I. Stiell, J.F. Dreyer, M.J. Kovacs.
Analysis and interpretation of the data: P.S. Wells, D.R. Anderson, M. Rodger, I. Stiell, M. Forgie, M.J. Kovacs.
Drafting of the article: P.S. Wells, D.R. Anderson, M. Rodger, I. Stiell, J.F. Dreyer, D. Barnes, M. Forgie, J. Ward.
Critical revision of the article for important intellectual content: P.S. Wells, D.R. Anderson, M. Rodger, D. Barnes, M. Forgie, G. Kovacs, J. Ward, M.J. Kovacs.
Final approval of the article: P.S. Wells, D.R. Anderson, M. Rodger, I. Stiell, D. Barnes, M. Forgie, G. Kovacs, J. Ward, M.J. Kovacs.
Provision of study materials or patients: P.S. Wells, D.R. Anderson, M. Rodger, I. Stiell, D. Barnes, M. Forgie, G. Kovacs, J. Ward, M.J. Kovacs.
Statistical expertise: P.S. Wells.
Obtaining of funding: P.S. Wells, D.R. Anderson, G. Kovacs.
Administrative, technical, or logistic support: P.S. Wells, J.F. Dreyer, G. Kovacs, M.J. Kovacs.
Collection and assembly of data: P.S. Wells, D.R. Anderson, M.J. Kovacs.
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