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This prospective management trial with a 3 month follow up examined whether the use of multidetector row computed tomographic (CT) scanning combined with d-dimer ruled out pulmonary embolism (PE) safely without the use of lower limb ultrasonography, which has previously been shown to be needed along with single detector row CT scanning.
756 patients (of the 1014 screened: exclusion criteria included contraindications to contrast CT and other reasons for not participating in the study) attending the emergency departments of three teaching hospitals were investigated with a standard sequential protocol; 194 (26%) were found to have PE. Of 82 patients with a high clinical probability, 78 had PE on the CT scan, one had a proximal deep vein thrombosis (DVT) with a negative CT scan, and three had negative ultrasound and CT scans as well as negative angiography. Of the remaining 674 patients without a high clinical probability of PE, 232 (34%) had a negative d-dimer assay and an uneventful follow up. CT scanning showed PE in 109 patients, proximal DVT on ultrasonography with negative CT was found in two patients, and both CT scanning and ultrasonography were negative in 318 patients. The overall 3 month risk of thromboembolism among the 523 patients who did not have PE and were not receiving treatment was 1.0% (95% CI 0.4 to 2.2). Even with the addition of the three patients with proximal DVT on ultrasonography and negative findings on CT scanning, the maximum 3 month risk would have been 1.5% (95% CI 0.8 to 3.0) if ultrasonography had not been included in the work up. This study indicates the potential clinical use of a diagnostic strategy using d-dimer assay and multidetector row CT scanning for ruling out PE without lower limb ultrasonography.
The limitations of the study include the large number of patients (25%) excluded, so the results may not yet be generalisable. It was also not a true outcome study since venous ultrasonography was performed in all patients with an abnormal d-dimer level and those with DVT and no PE on CT scanning were anticoagulated. The results of this study will need evaluation in a proper outcome study where the decision to anticoagulate is made on the basis of CT scan results alone.
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