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Br J Radiol. 2012 Jan;85(1009):37-43. doi: 10.1259/bjr/17451818. Epub 2011 Sep 21.

Pulmonary embolism: investigation of the clinically assessed intermediate risk subgroup.

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Radiology Department, Royal Hallamshire Hospital, Sheffield NHS Teaching Hospitals Trust, Sheffield, UK.



The simplified Wells pre-test probability scoring algorithm for pre-investigation evaluation of pulmonary emboli (PE) is a commonly utilised and validated assessment tool. We sought to identify whether use of a dichotomised scoring system altered the overall negative predictive value (NPV) in patients referred for CT pulmonary angiography (CTPA) assessment of suspected PE.


Prospective data collection of all patients referred for CTPA evaluation of suspected acute PE during a 3 year period was carried out. Pre-test risk stratification was performed according to simplified Wells criteria in conjunction with plasma d-Dimer (Bio-Pool and IL test) estimation. Retrospective dichotomisation was also performed.


2531 patients were investigated for suspected acute PE; acute thromboemboli were confirmed in 22.7%. The overall NPV for negative d-Dimer and intermediate pre-test probability (PTP) was 98.9% [95% confidence interval (CI) 96.3-99.7%]; with retrospective dichotomisation, the NPV for the PE unlikely group was 99.0% (95% CI 94.8-99.8%). Implementation of dichotomised scoring, excluding PE unlikely with negative d-Dimer cases from further imaging, would have yielded a 4% reduction in CTPA referral pathway imaging at our institution.


We demonstrate no significant difference between exclusion in the intermediate subgroup and the retrospectively dichotomised PE unlikely group and demonstrate the high negative predictive power of the Bio-Pool and IL tests in conjunction with the Wells PTP tool. Prior to implementation of new guidelines for exclusion of patients with suspected PE from further imaging, hospitals should audit their own practice and validate the d-Dimer assay utilised at their institution.

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