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

TLDR

Diagnostic strategies combining ultrasound, D‑dimer measurement, and clinical probability have proven safe but have not been compared in randomized trials for patients with suspected lower‑extremity deep‑vein thrombosis. In a randomized trial, clinicians first classified outpatients as likely or unlikely for DVT using a clinical model, then assigned them to either ultrasound alone or to D‑dimer testing followed by ultrasound only if the D‑dimer was positive or the patient was clinically likely. The study found a 15.7 % prevalence of DVT or pulmonary embolism, and D‑dimer testing reduced ultrasound use from 1.34 to 0.78 tests per patient, with 39 % of patients avoiding imaging and no increase in adverse events.

Abstract

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.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.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.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.