Low clinical pretest probability (C-PTP) and a ?-dimer of less than 1,000 ng/mL identify patients with a low risk for pulmonary embolism, according to a study published in the issue of the New England Journal of Medicine.

Clive Kearon, Ph.D., from McMaster University in Hamilton, Ontario, Canada, and colleagues performed a prospective study in which pulmonary embolism was considered to be ruled out without further testing in outpatients with low C-PTP and ?-dimer <1,000 ng/mL or with moderate C-PTP and ?-dimer <500 ng/mL. All other patients underwent chest imaging. A total of 2,017 patients were enrolled, 7.4 percent of whom had pulmonary embolism on initial diagnostic testing.

The researchers found that none of the 1,325 patients with low or moderate C-PTP (1,285 and 40 patients, respectively) had venous thromboembolism during three-month follow-up. These patients included 315 with low C-PTP and a ?-dimer level of 500 to 999 ng/mL. Venous thromboembolism occurred in one of the 1,863 patients who did not receive a diagnosis of pulmonary embolism initially and did not receive anticoagulant therapy. The strategy used resulted in use of chest imaging in 34.3 percent of patients compared with 51.9 percent with a diagnostic strategy in which pulmonary embolism is ruled out with low C-PTP and a ?-dimer level of <500 ng/ml.

"This way of using ?-dimer testing and clinical assessment reduced the need for computed tomography scanning by one-third," Kearon said in a statement.

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