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Stein PD, et al. "Multidetector Computed Tomography for Acute Pulmonary Embolism". The New England Journal of Medicine. 2006. 354(22):2317-2327.
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Clinical Question

In patients with clinically suspected acute pulmonary embolism, what is the diagnostic accuracy of CT angiography for the diagnosis of acute pulmonary embolism?

Bottom Line

PIOPED II demonstrated an 83% sensitivity and 96% specificity with CT angiography in detecting acute pulmonary embolism.

Major Points

PIOPED II (2006) is the largest study to date which compared CT angiography (CTA) against a composite reference standard and demonstrated an 83% sensitivity and 96% specificity in detecting an acute pulmonary embolism (PE). In addition, PIOPED II suggested that the predictive value of CTA is highly concordant with the pretest clinical probability of PE using Well's criteria.


  • Prospective, multicenter, comparison study
  • 7,284 screened, 3,262 eligible, 1,090 enrolled
  • N=824 completed evaluation for diagnosis of PE by both:
    • Composite reference standard, and
    • CT angiography
  • Setting: 8 clinical centers
  • Enrollment: 2001-2003


Inclusion Criteria

  • At least 18 years of age
  • Clinically suspected acute PE

Exclusion Criteria

  • Unable to complete testing within 36 hours
  • Elevated creatinine levels or receiving dialysis
  • History of long-term anticoagulant use
  • Critically ill or receiving ventilatory support
  • Allergic to contrast agents
  • MI within preceding month
  • VF or sustained VT within 24 hours
  • Planned to have thrombolytic therapy within next 24 hours
  • IVC filter in situ
  • Upper extremity DVT
  • In prison
  • Possible pregnancy


  • Prior to CTA, pretest probability of PE calculated by clinical assessment, including Wells score.
  • Criteria for diagnosis of acute PE by composite reference standard:
    • V-Q scan showed high probability of PE in patient with no history of PE
    • Abnormal findings on venous compression ultrasonography of lower extremities
    • Abnormal findings on pulmonary digital-subtraction angiography (DSA)
  • Criteria for exclusion of acute PE via composite reference standard:
    • Normal findings on V-Q scan, or venous ultrasonography, or DSA
    • V-Q scan showed either low or very low probability of PE
    • Clinical Wells score of less than 2
  • Criteria for diagnosis of acute PE by CTA:
    • Failure of contrast material to fill entire lumen because of central filling defect
    • Partial filling defect
    • Peripheral intra-luminal filling defect
  • Criteria for diagnosis of acute DVT by venous phase imaging (CTV): complete or partial central filling defect


Diagnosis by composite reference standard
PE diagnosed in 32%
94% of excluded had followup CTA at 6 months, and <1% received anticoagulant agents
Diagnosis by CTA
94% received adequate CTA for conclusive interpretation and used in calculation of diagnostic accuracy
Sensitivity: 83%
Specificity: 96%
NPV: 95%
PPV: 86%
97% for main or lobar artery
68% for segmental vessel
25% for subsegmental branch
Diagnosis by CTA-CTV
89% received adequate CTA-CTV for conclusive interpretation and used in calculation of diagnostic accuracy
Sensitivity: 90%
Specificity: 95%
NPV: 97%
PPV: 85%
3% in inferior vena cava or pelvic veins
85% in thigh veins alone
12% in both inferior vena cava or pelvic veins and thigh veins
Incorporating clinical assessment
Predictive value of CTA varied substantially when clinical assessment, including Well's score, was taken into account
PPV of PE in patients with positive CTA and high, intermediate or low clinical probability was 96, 92, 58%, respectively.
NPV of PE in patients with negative CTA and low, intermediate, or high clinical probability was 96, 89, 60%, respectively.

Adverse Events

  • Mild allergic reaction (itching, swollen eyelid, vomiting), urticaria, moderately severe extravasation of contrast material in <1% CTA procedures
  • One patient with diabetes mellitus had transient episode of AKI after CTA-CTV


  • Sensitivity was based on number of patients who had conclusive interpretations of CTA or CTA-CTV. Sensitivity would be lower if patients with inconclusive interpretations (owing to poor image quality) were included.
  • Data reported with four-slice CT. Advanced scanners with 8-slice or 16-slice scanners were not studied.
  • Not all patients received pulmonary angiography; V/Q scan or LE ultrasound could also determine positive or negative disease status
  • The false negative rate (17%) was higher than anticipated[1]
  • It's unclear if the accuracy will be affected if the clinical suspicion comes from a trainee rather than a seasoned clinician[2]
  • The double reading by radiologists is unrealistic[2]


Sponsored by the National Heart, Lung, and Blood Institute.

Further Reading