Subsequent pulmonary embolism: risk after a negative helical CT pulmonary angiogram--prospective comparison with scintigraphy

Radiology. 2000 May;215(2):535-42. doi: 10.1148/radiology.215.2.r00ma23535.


Purpose: 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.

Materials and 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.

Conclusion: 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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Analysis of Variance
  • Angiography / methods
  • Anticoagulants
  • Chi-Square Distribution
  • Contraindications
  • Female
  • Follow-Up Studies
  • Hospitalization
  • Humans
  • Image Processing, Computer-Assisted / methods
  • Logistic Models
  • Lung / blood supply*
  • Lung / diagnostic imaging
  • Male
  • Multivariate Analysis
  • Predictive Value of Tests
  • Probability
  • Prospective Studies
  • Pulmonary Embolism / diagnostic imaging
  • Pulmonary Embolism / etiology*
  • Radionuclide Imaging
  • Radiopharmaceuticals*
  • Reproducibility of Results
  • Risk Factors
  • Safety
  • Survival Rate
  • Tomography, X-Ray Computed / methods*
  • Ventilation-Perfusion Ratio


  • Anticoagulants
  • Radiopharmaceuticals