Prospective studies that evaluated computed tomography (CT) pulmonary angiography in consecutive increased risk patients, identified through a diagnostic strategy based on a clinical decision rule and D-dimer test without additional imaging tests prior to CT pulmonary angiography, were eligible for inclusion. Studies that assessed the additional value of compression ultrasonography performed after a negative CT pulmonary angiography test for excluding venous thromboembolism were also eligible. Eligible studies were required to report predefined endpoints, have a clear description of inclusion and exclusion criteria, and have clinical follow-up of greater than one month.
The primary outcome was the negative predictive value of CT pulmonary angiography and the safety of withholding anticoagulant therapy on the basis of a normal CT pulmonary angiography result. Endpoints for safety were the incidence of confirmed adverse thrombotic events subsequent to a normal CT pulmonary angiography result, including all occurrences of venous thromboembolism (both pulmonary embolism and deep vein thrombosis), and mortality attributable to pulmonary embolism.
The mean age of included patients ranged from 50 to 60 years; the proportion of males ranged from 35 to 46%. Most included patients were outpatients. Different clinical decision rules were used to identify patients with an increased risk of pulmonary embolism (the Geneva Score, revised Geneva Score, the Wells rule and the Hyers criteria). All studies also used D-dimer, although the assay varied across studies. Some studies used single-detector CT; others used multi-detector row CT modalities.
Two reviewers independently assessed studies for inclusion. Disagreements were resolved through referral to a third reviewer.