Comparing the diagnostic performance of 2 clinical decision rules to rule out deep vein thrombosis in primary care patients.
OBJECTIVE
The Wells rule is widely used for clinical assessment of patients with suspected deep vein thrombosis (DVT), especially in the secondary care setting. Recently a new clinical decision rule for primary care patients (the primary care rule) has been proposed, because the Wells rule is not sufficient to rule out DVT in this setting. The objective was to compare the ability of both rules to safely rule out DVT and to efficiently reduce the number of referrals for leg ultrasound investigation that would result in a negative finding.


METHODS
Family physicians collected data on 1,086 patients to calculate the scores for both decision rules before leg ultrasonography was performed. In all patients D-dimer (dimerized plasmin fragment D) testing was performed using a rapid point-of-care assay. Patients were stratified into risk categories defined by each rule and the D-dimer result. Outcomes were DVT (diagnosed by ultrasonography) and venous thromboembolic complications or death caused by a possible thromboembolic event during a 90-day follow-up period. We calculated the differences between the 2 rules in the number of missed diagnoses and the proportions of patients that needed ultrasound testing.


RESULTS
Data from 1,002 eligible patients were used for this analysis. A venous thromboembolic event occurred during follow-up in 7 patients with a low score and negative D-dimer finding, both with the Wells rule (7 of 447; 1.6%; 95% confidence interval [CI], 0.7%-3.3% ) and the primary care rule (7 of 495; 1.4%; 95% CI, 0.6%-3.0%). Using the Wells rule, 447 patients (45%) would not need referral for further testing compared with 495 patients (49%) when using the primary care rule (McNemar P <.001).


CONCLUSIONS
In primary care, suspected DVT can safely be ruled out using either of the 2 rules in combination with a point-of-care D-dimer test. Both rules can reduce unnecessary referrals for compression ultrasonography by about 50%, though the primary care rule reduces it slightly more.
Department of General Practice, Vascular Medicine and Clinical Epidemiology, University of Amsterdam, The Netherlands. e.f.vandervelde@amc.uva.nl
Eit Frits
EF
van der Velde
Diane B
DB
Toll
Arina J
AJ
Ten Cate-Hoek
Ruud
R
Oudega
Henri E J H
HE
Stoffers
Patrick M
PM
Bossuyt
Harry R
HR
Büller
Martin H
MH
Prins
Arno W
AW
Hoes
Karel G M
KG
Moons
Henk C P M
HC
van Weert
D003661:Decision Support Techniques; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis*; D006801:Humans; D008297:Male; D008487:Medical History Taking; D008875:Middle Aged; D009426:Netherlands; D011237:Predictive Value of Tests; D011320:Primary Health Care / Q000379:methods*; D012307:Risk Factors; D014463:Ultrasonography; D020246:Venous Thrombosis / Q000097:blood / Q000175:diagnosis* / Q000000981:diagnostic imaging*
D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D
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