Tuy nhiên, nó không phải là rõ ràng cho dù kháng đông được khấu trừ ở những bệnh nhân với xác suất thấp quét trong nghiên cứu này. Một hệ thống xem xét lại bởi van Beek et al. (13) báo cáo tiêu cực và tích cực giá trị dự báo 99,7% | 404 K. Juluru and J. Eng However it is not clear whether anticoagulation was withheld in patients with low-probability scans in this study. One systematic review by van Beek et al. 13 reported negative and positive predictive values of and 88 respectively. C. Modality 3 Computed Tomography Pulmonary Angiography Scanners with Fewer than Four Detectors Summary of Evidence Computed tomography pulmonary angiography CTPA is increasingly being used for the diagnosis of PE. Level I strong evidence studies using a clinical outcome reference standard find rates of PE recurrence to be 0 to 6 with negative predictive values of 94 to 100 . Studies using a conventional pulmonary angiography reference standard find broad variations in sensitivities specificities and positive and negative predictive values likely due to variations in detection of sub-segmental emboli. Despite these variations there is strong evidence to show that it is safe to withhold anticoagulation in patients with negative CTPA. Supporting Evidence A systematic review of all published literature from 1966 to 2003 Eng et al. in press identified eight primary prospective levels I to II strong to moderate evidence studies in which all subjects underwent both CTPA and conventional angiography the latter being considered the reference standard. Among the eight primary studies the sensitivities ranged from 45 to 100 and specificities ranged from 78 to 100 . Nine major studies were found in our search that evaluated the negative predictive value of CTPA using clinical outcomes. One prospective level I strong evidence study with a total PE prevalence of 25 followed 378 patients with negative CTPA for 3 months 14 . No patients were lost to follow-up none were anticoagulated during the follow-up period and no patients were excluded for other reasons. Four of the 378 patients developed PE recurrence rate 1 negative predictive value 99 . In all studies recurrence rates ranged from 0 to 6 and negative predictive .
