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D-Dimer Testing Helps Identify Deep-Vein Thrombosis, Reduces Need for Further Ultrasound In Those With Negative Findings

In patients with suspected deep-vein thrombosis, the combination of clinical judgment and testing for _D-dimer, a marker of endogenous fibrinolysis, effectively identifies those patients clinically likely and unlikely to have deep-vein thrombosis.

This diagnostic strategy eliminates the need for ultrasound testing in patients with both a negative _D-dimer test and a negative clinical judgment while those with positive findings can be referred for ultrasound.

"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," writes Philip S. Wells, MD, University of Ottawa, Ontario, Canada, and colleagues. They clinically evaluated a cohort of patients (mean age about 58 years, mean duration of symptoms over 7 days) to predict their probability of deep-vein thrombosis and then randomised 530 patients to undergo ultrasound imaging alone (control group) and 566 patients to undergo _D-dimer testing followed by ultrasound only after finding positive clinical and _D-dimer tests.

Over 3 months, among the 1082 patients who completed follow up, proximal deep-vein thrombosis or pulmonary embolism was reported in 83 of the control group and 87 in the _D-dimer group for an overall prevalence of 15.7%.

The investigators report that among patients ruled as unlikely to have deep-vein thrombosis, there were 2 confirmed thromboembolic events in the _D-dimer group (0.4%) and 6 events in the control group (1.4%).

Overall, the mean number of ultrasound tests per patient was 0.78 in the _D-dimer group and 1.34 in the control group. Ultrasound imaging was not required in 39% of the patients in the _D-dimer group which resulted in a significant reduction in ultrasound testing.

The diagnostic algorithm using _D-dimer testing established a definitive diagnosis on the day of presentation in 82% of the patients while a definitive diagnosis was established in only 65% of the control group.

"In patients who are considered clinically unlikely to have deep-vein thrombosis and who have a negative _D-dimer test," the authors conclude, "the diagnosis of deep-vein thrombosis can safely be excluded without the need for further diagnostic testing."

N Engl J Med 2003;349:13:1227-35.

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