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Predicting Deep Venous Thrombosis in Pregnancy: Out in “LEFt” Field?
- Wee-Shian Chan, MD, MSc;
- Agnes Lee, MD, MSc;
- Frederick A. Spencer, MD;
- Mark Crowther, MD, MSc;
- Marc Rodger, MD, MSc;
- Tim Ramsay, MSc, PhD; and
- Jeffrey S. Ginsberg, MD
- From Women's College Hospital, Toronto; Hamilton Health Sciences Corporation, McMaster University Medical Centre, and St. Joseph's Hospital, Hamilton; and The Ottawa Hospital and Ottawa Health Research Institute, Ottawa, Ontario, Canada.
Abstract
Background: Clinicians' assessment of pretest probability, based on subjective criteria or prediction rules, is central to the diagnosis of deep venous thrombosis (DVT). Pretest probability assessment for DVT diagnosis has never been evaluated in pregnant women.
Objective: To evaluate the accuracy of clinicians' subjective assessment of pretest probability for DVT diagnosis and identify prediction variables that could be used for pretest probability assessment in pregnant women with suspected DVT.
Design: A cross-sectional study conducted over 7 years (March 2000 to April 2007).
Setting: 5 university-affiliated, tertiary care centers in Canada.
Patients: 194 unselected pregnant women with suspected first DVT.
Intervention: Diagnosis of DVT was established with abnormal compression ultrasonography at presentation or on serial imaging. Pretest probability by subjective assessment was recorded by thrombosis experts for each patient before knowledge of results.
Measurements: The sensitivity, specificity, negative predictive value, and likelihood ratios of subjective pretest probability assessment and their corresponding 95% CIs were calculated on the basis of the diagnosis of DVT. Patients were DVT positive if they had diagnostic compression ultrasonography at initial or serial testing or symptomatic venous thromboembolism on follow-up. Patients were DVT negative if they had negative compression ultrasonography at presentation and no venous thromboembolism on follow-up. A prediction rule for assessing DVT was derived, and an internal validation study was done to explore its performance.
Results: The prevalence of DVT was 8.8%. Clinicians' subjective assessment of pretest probability categorized patients into 2 groups: low pretest probability (two thirds of patients) with a low prevalence of DVT (1.5% [95% CI, 0.4% to 5.4%]) and a negative predictive value of 98.5% (CI, 94.6% to 99.6%), and nonlow pretest probability with a higher prevalence of DVT (24.6% [CI, 15.5% to 36.7%]). Three variables (symptoms in the left leg [L], calf circumference difference ≥2 cm [E], and first trimester presentation [Ft]) were highly predictive of DVT in pregnant patients.
Limitations: Few outcomes occurred. Altogether, 17 events were diagnosed during the study. The prediction rule derived should be validated on an independent sample before applying it to clinical practice.
Conclusion: Subjective assessment of pretest probability seems to exclude DVT when the pretest probability is low. Moreover, 3 objective variables (“LEFt”) may improve the accuracy of the diagnosis of DVT in pregnancy. Prospective validation studies are needed.
Primary Funding Source: Heart and Stroke Foundation of Ontario.
Article and Author Information
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Acknowledgment: The authors acknowledge the contributions of Anne Marie Clement, Pam Stevens, and Myriel Quilacio for assistance in the study.
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Grant Support: Partial funding by the Heart and Stroke Foundation of Ontario (grant NA 5048) to recruit half of the patients in the cohort.
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Potential Financial Conflicts of Interest: None disclosed.
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Reproducible Research Statement: Study protocol: Available from Dr. Chan (e-mail, wee-shian.chan{at}wchospital.ca). Statistical code and data set: Not available.
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Requests for Single Reprints: Wee-Shian Chan, MD, MSc, Department of Medicine, Women's College Hospital, 76 Grenville Street, Toronto, Ontario M5G 1B2, Canada; e-mail, wee-shian.chan{at}wchospital.ca.
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Current Author Addresses: Dr. Chan: Department of Medicine, Women's College Hospital, 76 Grenville Street, Toronto, Ontario M5G 1B2, Canada.
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Dr. Lee: Hamilton Health Sciences Corporation, Henderson General Division, 711 Concession Street, Hamilton, Ontario L8V 1C3, Canada.
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Drs. Spencer and Ginsberg: McMaster University Medical Centre, 1200 Main Street West, HSC-3X28, Hamilton, Ontario L8N 3Z5, Canada.
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Dr. Crowther: St. Joseph's Hospital, Room L 208-4, 50 Charlton Avenue East, Hamilton, Ontario L8N 4A6, Canada.
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Dr. Rodger: Division of Hematology, The Ottawa Hospital, General Campus, 501 Smyth Road, Ottawa, Ontario K1H 8L6, Canada.
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Dr. Ramsay: Ottawa Health Research Institute, 725 Parkdale Avenue, Ottawa, Ontario K1Y 4E9, Canada.
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Author Contributions: Conception and design: W.S. Chan, A. Lee, J.S. Ginsberg.
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Analysis and interpretation of the data: W.S. Chan, A. Lee, M. Crowther, M. Rodger, T. Ramsay, J.S. Ginsberg.
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Drafting of the article: W.S. Chan, A. Lee, F.A. Spencer, M. Crowther, M. Rodger, J.S. Ginsberg.
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Critical revision of the article for important intellectual content: W.S. Chan, A. Lee, F.A. Spencer, M. Crowther, M. Rodger, T. Ramsay, J.S. Ginsberg.
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Final approval of the article: W.S. Chan, A. Lee, F.A. Spencer, M. Rodger, T. Ramsay, J.S. Ginsberg.
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Provision of study materials or patients: W.S. Chan, M. Crowther, M. Rodger, J.S. Ginsberg.
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Statistical expertise: W.S. Chan, M. Rodger, T. Ramsay, J.S. Ginsberg.
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Obtaining of funding: W.S. Chan, A. Lee, M. Rodger.
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Administrative, technical, or logistic support: W.S. Chan, M. Rodger.
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Collection and assembly of data: W.S. Chan.
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