Comparing the Diagnostic Performance of 2 Clinical Decision Rules to Rule Out Deep Vein Thrombosis in Primary Care Patients

PURPOSE 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 suffi cient to rule out DVT in this setting. The objective was to compare the ability of both rules to safely rule out DVT and to effi ciently reduce the number of referrals for leg ultrasound investigation that would result in a negative fi nding. 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 stratifi ed into risk categories defi ned by each rule and the D-dimer result. Outcomes were DVT (diagnosed by ultrasonog- raphy) and venous thromboembolic complications or death caused by a possible thromboembolic event during a 90-day follow-up period. We calculated the dif- ferences between the 2 rules in the number of missed diagnoses and the propor- tions 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 fi nding, both with the Wells rule (7 of 447; 1.6%; 95% confi dence 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 pri- mary 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.