In an adult without contraindications, will a contrast‑enhanced computed tomography pulmonary angiography (CTPA) reliably rule out pulmonary embolism?

Will CT with Contrast Rule Out PE?

Yes, a good quality negative CTPA (CT pulmonary angiography with contrast) can reliably rule out pulmonary embolism in most patients and does not require further investigation or treatment for PE. 1

Diagnostic Performance

CTPA is the recommended first-line imaging test for suspected PE, with proven safety in ruling out the disease. 1, 2

• Sensitivity: 83% and specificity: 96% for PE diagnosis, with excellent visualization of pulmonary arteries down to the subsegmental level 1
• Negative predictive value varies by clinical probability:
  • Low clinical probability: 96% 1
  • Intermediate clinical probability: 89% 1
  • High clinical probability: only 60% 1
• 3-month recurrence rate after negative CTPA: 1.1%, which compares favorably to the 0.9% recurrence rate after negative conventional pulmonary angiography 1

Critical Distinction: CTPA vs Standard CT Chest

Standard "CT with contrast" is NOT the same as CTPA. 2

• CTPA uses specialized acquisition timing optimized for peak pulmonary arterial enhancement 2
• CTPA includes multiplanar reconstructions and 3D renderings specifically designed to evaluate the pulmonary arterial tree 2
• Standard CT chest protocols are not optimized for pulmonary vascular visualization and should not be used to rule out PE 2

When CTPA Reliably Rules Out PE

Patients with good quality negative CTPA do not require further investigation or treatment for PE. 1

• Safe to withhold anticoagulation after negative CTPA in patients with low or intermediate clinical probability 1, 3
• Pooled negative predictive value of 98.8% (95% CI 98.2-99.2) when used as sole test 3
• No additional compression ultrasonography of legs is needed after negative CTPA 3

Important Caveats

High clinical probability with negative CTPA requires caution. 1

• Consider further testing if there is discordance between high clinical suspicion and negative CTPA result 1
• The negative predictive value drops to 60% in patients with high pre-test probability 1
• Clinical judgment should guide whether additional imaging is needed in this scenario 1

Technical quality matters critically. 1

• Meticulous attention to contrast timing is essential to achieve results comparable to published series 1
• A small proportion of examinations are technically unsatisfactory in all published series 1
• Contrast opacification of at least 210 Hounsfield units is needed for reliable interpretation 4
• Only good quality negative CTPA studies can safely exclude PE 1

Alternative Imaging When CTPA Cannot Be Performed

Ventilation-perfusion (V/Q) scan is the preferred alternative when CTPA is contraindicated. 1, 5

• Use V/Q scan in patients with severe renal failure, contrast allergy, or pregnancy 1, 5
• Normal V/Q scan has high negative predictive value for excluding PE 5
• V/Q scan is lower radiation and contrast-sparing compared to CTPA 1