A Red Blood Cell Agglutination D-Dimer Test to Exclude Deep Venous Thrombosis in Pregnancy

7 August 2007 | Volume 147 Issue 3 | Pages 165-170

Background: D-Dimer testing is often used with compression ultrasonography for the diagnosis of deep venous thrombosis (DVT) in nonpregnant patients. The D-dimer test is highly sensitive, and a negative result can obviate the need for further testing for DVT. This test has not been studied for DVT diagnosis in pregnancy because its specificity was deemed too poor.

Objective: To determine the sensitivity and specificity and assess the utility of the SimpliRED assay (Agen Biomedical, Brisbane, Australia) for the diagnosis of DVT in pregnant women.

Design: Prospective cohort study.

Setting: 5 tertiary university-affiliated Canadian hospitals providing care to obstetric patients.

Patients: 149 consecutive pregnant women with suspected DVT who presented to 1 of the participating centers over 5 years.

Intervention: Participating women were tested with compression leg ultrasonography (single or serially on days 0, 3, and 7) and received 3 months' clinical follow-up for the presence or absence of DVT. Whole blood was tested with the SimpliRED assay at initial presentation, and results were correlated with ultrasonography and clinical findings for the presence or absence of DVT.

Measurements: The sensitivity, specificity, and negative predictive value of the SimpliRED assay were calculated, along with the prevalence of false-positive SimpliRED assay results (with 95% CIs).

Results: The prevalence of DVT in the cohort was 8.7% (95% CI, 5.2% to 14.4%). The sensitivity of the SimpliRED assay was 100% (CI, 77% to 100% [13 of 13 patients]), the specificity was 60% (CI, 52% to 68% [81 of 135]), and the negative predictive value was 100% (CI, 95% to 100% [81 of 81]). The SimpliRED assay was positive in 0% (CI, 0% to 60%), 24% (CI, 14% to 37%), and 51% (CI, 40% to 61%) of women in the first, second, and third trimesters, respectively, among pregnant patients in whom DVT was not diagnosed.

Limitations: The prevalence of DVT in the cohort was low, resulting in wide CIs. The clinician's previous impression was used to determine pretest probability in the absence of a validated clinical prediction rule for pregnant women.

Conclusion: The SimpliRED assay may be useful in pregnancy because a normal result excludes DVT and occurs frequently enough to be clinically helpful.

Editors' Notes Context Because D-dimer levels increase with pregnancy D-dimer testing is thought to be less accurate for excluding venous thromboembolism in pregnant women than in nonpregnant women. Contribution In this observational, cross-sectional study of 149 pregnant women with suspected deep venous thrombosis (DVT), 13 women (8.7%) had documented DVT. All 13 women with DVT had a positive result on the SimpliRED D-dimer assay (sensitivity, 100% [95% CI, 77% to 100%]). Cautions The lower bound of the 95% CI for the sensitivity of the SimpliRED assay was relatively low (77%). Caution is indicated when the assay is negative and clinical suspicion is relatively high. Implications The SimpliRED assay appears to be as useful for evaluating suspected DVT in pregnant women as in nonpregnant women. A normal result excludes the diagnosis. —The Editors

 

Author and Article Information

From Women's College Hospital, Toronto, Ontario, Canada; North Shore Hospital, Takapuna, New Zealand; McMaster University, Hamilton, Ontario, Canada; and the University of Ottawa, Ottawa, Ontario, Canada.

Acknowledgment: The authors thank Agen Biomedical for providing the SimpliRED assay kits.

Grant Support: Partial funding was provided over 2 years by the Heart and Stroke Foundation of Ontario (grant NA 5048) to recruit patients into the study. Dr. Ginsberg is a recipient of a Career Investigator Award from the Heart and Stroke Foundation of Ontario.

Potential Financial Conflicts of Interest: Grants received: S. Chunilal (Agen Biomedical).

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.

Current Author Addresses: Dr. Chan: Department of Medicine, Women's College Hospital, 76 Grenville Street, Toronto, Ontario M5G 1B2, Canada.

Dr. Chunilal: North Shore Hospital, PO Box 93-503, Takapuna, Auckland, New Zealand.

Dr. Lee: Henderson General Division, Hamilton Health Sciences Corp., 711 Concession Street, Hamilton, Ontario L8V 1C3, Canada.

Dr. Crowther: St. Joseph's Hospital, Room L 208-4, 50 Charlton Avenue East, Hamilton, Ontario L8N 4A6, Canada.

Dr. Rodger: Division of Hematology, The Ottawa Hospital General Campus, 501 Smyth Road, Ottawa, Ontario K1H 8L6, Canada.

Dr. Ginsberg: McMaster University Medical Centre, 1200 Main Street West, HSC-3W11, Hamilton, Ontario L8N 3Z5, Canada.

Author Contributions: Conception and design: W.S. Chan, S. Chunilal, A. Lee, M. Rodger.

Analysis and interpretation of the data: W.S. Chan, S. Chunilal, A. Lee, M. Rodger.

Drafting of the article: W.S. Chan, J.S. Ginsberg.

Critical revision of the article for important intellectual content: W.S. Chan, A. Lee, M. Rodger, J.S. Ginsberg.

Final approval of the article: W.S. Chan, A. Lee, M. Rodger, J.S. Ginsberg.

Provision of study materials or patients: W.S. Chan, S. Chunilal, A. Lee, M. Crowther, M. Rodger.

Statistical expertise: S. Chunilal, M. Rodger.

Obtaining of funding: W.S. Chan, S. Chunilal, M. Crowther, M. Rodger.

Administrative, technical, or logistic support: M. Rodger.

Collection and assembly of data: W.S. Chan, M. Crowther, M. Rodger.

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