D-dimer testing as an adjunct to ultrasonography in patients with clinically suspected deep vein thrombosis: prospective cohort study

OBJECTIVE: To investigate the efficacy of using a rapid plasma D-dimer test as an adjunct to compression ultrasound for diagnosing clinically suspected deep vein thrombosis. DESIGN: D-dimer concentrations were determined in all patients with a normal ultrasonogram at presentation. Repeat ultrasonography was performed 1 week later only in patients with abnormal D-dimer test results. MAIN OUTCOME AND MEASURES: Patients with normal ultrasonograms were not treated with anticoagulants and were followed for 3 months for thromboembolic complications. SETTING: University research and affiliated centres. SUBJECTS: 946 patients with clinically suspected deep vein thrombosis. RESULTS: Ultrasonograms were abnormal at presentation in 260 (27.5%) patients. Of the remaining 686 patients tested for D-dimer, 88 (12.8%) had abnormal concentrations. During follow up venous thromboembolic complications occurred in one of the 598 patients who were not treated with anticoagulants and who had an initial normal ultrasonogram and D-dimer concentration, whereas thromboembolic complications occurred in two of the 83 untreated patients who had abnormal D-dimer concentrations but a normal repeat ultrasonogram. The cumulative incidence of venous thromboembolic complications during follow up was 0.4% (95% confidence interval 0% to 0.9%). The rapid plasma D-dimer test used as an adjunct to compression ultrasonography resulted in a reduction in the mean number of repeat ultrasound examinations and additional hospital visits from 0.7 to 0.1 per patient. CONCLUSIONS: Testing for D-dimer as an adjunct to a normal baseline ultrasound examination decreased the number of subsequent ultrasound examinations considerably without any increased risk of venous thromboembolic complications in patients not receiving anticoagulants. The use of ultrasound and testing for D-dimer enabled treatment decisions to be made at the time of presentation in most patients.