title: Subsequent pulmonary embolism: risk after a negative helical CT pulmonary angiogram--prospective comparison with scintigraphy.
abstract: OBJECTIVE
  To determine whether a helical computed tomographic (CT) scan that is negative for pulmonary embolism (PE) is a sufficiently reliable criterion to safely withhold anticoagulation therapy.
  
  
  METHODS
  Patients with negative helical CT scans were prospectively compared with patients with negative or low-probability scintigrams. In a 460-bed university hospital and clinic, 1,015 adult patients underwent either scintigraphy or helical CT for possible PE for 25 months. Five hundred forty-eight patients who had negative images and were not receiving anticoagulation therapy were prospectively followed up for 3 months for clinical, new imaging, death certificate, or autopsy evidence of subsequent PE. Ninety-seven patients were lost to follow-up.
  
  
  RESULTS
  Subsequent PE was found in two (1.0%) of 198 patients with negative CT scans, none of 188 patients with negative ventilation-perfusion (V-P) scans, and five (3.1%) of 162 patients with low-probability V-P scans (not statistically significant). Patients in the helical CT group were hospitalized more often, had more severe disease, had more substantial PE risk factors, and had a higher death rate. No deaths were attributed to PE in either group.
  
  
  CONCLUSIONS
  The frequency of clinical diagnoses of PE after a negative CT scan was low and similar to that after a negative or low-probability V-P scan. Helical CT is a reliable imaging tool for excluding clinically important PE.
authors.affiliation: Department of Radiology, Division of Pulmonary Medicine and Critical Care Medicine, 9200 W Wisconsin Ave, Milwaukee, USA. lgoodman@mcw.edu
authors.forename: L R
authors.initials: LR
authors.lastname: Goodman
authors.forename: R J
authors.initials: RJ
authors.lastname: Lipchik
authors.forename: R S
authors.initials: RS
authors.lastname: Kuzo
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.forename: T L
authors.initials: TL
authors.lastname: McAuliffe
authors.forename: D J
authors.initials: DJ
authors.lastname: O'Brien
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D000792:Angiography / Q000379:methods; D000925:Anticoagulants; D016009:Chi-Square Distribution; D000075202:Contraindications; D005260:Female; D005500:Follow-Up Studies; D006760:Hospitalization; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D016015:Logistic Models; D008168:Lung / Q000098:blood supply* / Q000000981:diagnostic imaging; D008297:Male; D015999:Multivariate Analysis; D011237:Predictive Value of Tests; D011336:Probability; D011446:Prospective Studies; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging / Q000209:etiology*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012307:Risk Factors; D012449:Safety; D015996:Survival Rate; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014692:Ventilation-Perfusion Ratio
chemical_list: D000925:Anticoagulants; D019275:Radiopharmaceuticals