Can a State-of-the-Art -Dimer Test Be Used to Determine the Need for CT Imaging in Patients Suspected of Having Pulmonary Embolism?

Rationale and Objectives The purpose of this study was to determine whether a simple rapid blood test can obviate computed tomography (CT) in a sizable percentage of patients suspected of having pulmonary embolism, based on the hypothesis that negative -dimer results could eliminate any further search for pulmonary embolism. Materials and Methods At the authors' institution, 2,121 sequential patients underwent a whole-blood antibody agglutination test for cross-linked fibrin degradation products (-dimer). Of these patients, 844 had positive test results and were not further considered. A retrospective review included reports of all multisection combined CT venographic and pulmonary angiographic studies obtained within 48 hours of the -dimer assay for the 1,277 patients with negative -dimer results; 229 (18%) of these 1,277 patients underwent combined CT venography and pulmonary angiography, usually within 24 hours. Results Retrospective review of the imaging examinations that were discrepant with the -dimer results revealed only three false-negative -dimer results. Of the 229 patients in whom combined CT venography and pulmonary angiography was performed for suspected pulmonary embolism, 226 (98.7%) had no evidence of acute pulmonary embolism or deep venous thrombosis. The negative predictive value of a negative -dimer result was therefore 98.7% (confidence interval, 96.2%-99.7%). Conclusion The -dimer assay is a simple rapid blood test that is sensitive to the presence of acute thrombosis. Very few patients with negative results have acute deep venous thrombosis or pulmonary embolism, with combined CT venography and pulmonary angiography used as the reference standard.