Predicting deep venous thrombosis in pregnancy: out in "LEFt" field?
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.


METHODS
A cross-sectional study conducted over 7 years (March 2000 to April 2007).


METHODS
5 university-affiliated, tertiary care centers in Canada.


METHODS
194 unselected pregnant women with suspected first DVT.


METHODS
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.


METHODS
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 > or = 2 cm [E], and first trimester presentation [Ft]) were highly predictive of DVT in pregnant patients.


CONCLUSIONS
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.


CONCLUSIONS
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.


BACKGROUND
Heart and Stroke Foundation of Ontario.
Chan
Wee-Shian
WS
Department of Medicine, Women's College Hospital, Toronto, Ontario, Canada. wee-shian.chan@wchospital.ca
Lee
Agnes
A
Spencer
Frederick A
FA
Crowther
Mark
M
Rodger
Marc
M
Ramsay
Tim
T
Ginsberg
Jeffrey S
JS
D003430:Cross-Sectional Studies; D004487:Edema / Q000473:pathology; D005260:Female; D006801:Humans; D007866:Leg / Q000473:pathology; D008487:Medical History Taking; D015999:Multivariate Analysis; D010808:Physical Examination; D011247:Pregnancy; D011250:Pregnancy Complications, Hematologic / Q000175:diagnosis* / Q000000981:diagnostic imaging; D011261:Pregnancy Trimester, First; D011336:Probability; D012307:Risk Factors; D012680:Sensitivity and Specificity; D014463:Ultrasonography; D020246:Venous Thrombosis / Q000175:diagnosis* / Q000000981:diagnostic imaging