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D-dimer Testing Can Help Diagnose Deep-Vein Thrombosis without Ultrasound

D-dimer testing can help clinicians decide which patients with suspected deep-vein thrombosis should have ultrasound imaging, without compromising patient safety.

Researchers from several medical centres in Canada conducted a randomised, control trial to test whether using D-dimer testing and clinical judgment in patients with suspected deep-vein thrombosis can safely reduce the need for ultrasound imaging.

In their study, Dr. Philip S. Wells, at the University of Ottawa, and colleagues evaluated nearly 1100 consecutive outpatients with suspected lower-extremity, deep-vein thrombosis using a clinical model to predict their likelihood of developing a thrombus. The investigators then randomly assigned the patients to receive either ultrasound imaging (530 patients) or D-dimer testing, followed by ultrasound (566 patients) -- unless the patient was considered clinically unlikely to have deep-vein thrombosis and the D-dimer test was negative.

"D-Dimer is a marker of endogenous fibrinolysis and should therefore be detectable in patients with deep-vein thrombosis," the researchers wrote. "Several studies have shown the D-dimer assay to have a high negative predictive value and D-dimer to be a sensitive but non-specific marker of deep-vein thrombosis."

The investigators found that the overall prevalence of deep-vein thrombosis or pulmonary embolism among all patients was 15.7%.

Among the patients for whom deep-vein thrombosis had been ruled out by the initial diagnostic strategy, there were 2 confirmed venous thromboembolic events in the D-dimer group (0.4%) and 6 events in the ultrasound control group (1.4%) during the 3-month follow-up period, the authors reported.

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. Two-hundred-and-eighteen patients (39%) in the D-dimer group did not require ultrasound imaging, they added.

"Suspected deep-vein thrombosis is a common condition, with a lifetime cumulative incidence of 2 to 5%," the investigators noted. "Untreated deep-vein thrombosis can result in pulmonary embolism, a potentially fatal outcome. Anticoagulant therapy reduces both morbidity and mortality from venous thromboembolism, and early diagnosis is therefore important. Accurate diagnosis of deep-vein thrombosis minimises the risk of thromboembolic complications and averts the exposure of patients without thrombosis to the risks of anticoagulant therapy."

"The addition of D-dimer testing to the diagnostic algorithm has the potential to make the diagnosis of deep-vein thrombosis in outpatients more convenient and economical," the researchers concluded. "In patients who are considered clinically unlikely to have deep-vein thrombosis and who have a negative D-dimer test, the diagnosis of deep-vein thrombosis can safely be excluded without the need for further diagnostic testing. Use of the D-dimer test also reduces the need for repeated ultrasound testing in patients who are likely to have deep-vein thrombosis and establishes a definitive diagnosis on the day of presentation in a larger proportion of patients."


N Engl J Med 2003;349:13:1227-35. "Evaluation of D-dimer in the diagnosis of suspected deep-vein thrombosis"

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