Evaluation of d -Dimer in the Diagnosis of Suspected Deep-Vein Thrombosis

background Several diagnostic strategies using ultrasound imaging, measurement of d -dimer, and assessment of clinical probability of disease have proved safe in patients with suspected deep-vein thrombosis, but they have not been compared in randomized trials. methods Outpatients presenting with suspected lower-extremity deep-vein thrombosis were potentially eligible. Using a clinical model, physicians evaluated the patients and categorized them as likely or unlikely to have deep-vein thrombosis. The patients were then randomly assigned to undergo ultrasound imaging alone (control group) or to undergo d -dimer testing ( d -dimer group) followed by ultrasound imaging unless the d -dimer test was negative and the patient was considered clinically unlikely to have deep-vein thrombosis, in which case ultrasound imaging was not performed. results Five hundred thirty patients were randomly assigned to the control group, and 566 to the d -dimer group. The overall prevalence of deep-vein thrombosis or pulmonary embolism was 15.7 percent. Among patients for whom deep-vein thrombosis had been ruled out by the initial diagnostic strategy, there were two confirmed venous thromboembolic events in the d -dimer group (0.4 percent; 95 percent confidence interval, 0.05 to 1.5 percent) and six events in the control group (1.4 percent; 95 percent confidence interval, 0.5 to 2.9 percent; P=0.16) during three months of follow-up. The use of d -dimer testing resulted in a significant reduction in the use of ultrasonography, from a mean of 1.34 tests per patient in the control group to 0.78 in the d -dimer group (P=0.008). Two hundred eighteen patients (39 percent) in the d- dimer group did not require ultrasound imaging. conclusions Deep-vein thrombosis can be ruled out in a patient who is judged clinically unlikely to have deep-vein thrombosis and who has a negative d -dimer test. Ultrasound testing can be safely omitted in such patients.