Which test is most definitive for pulmonary embolism?

• A. D-dimer
• B. CT pulmonary angiography
• C. V/Q scan
• D. Chest X-ray

Answer: (B)

CT pulmonary angiography most definitively confirms pulmonary embolism because it directly visualizes the pulmonary arteries after contrast, revealing a filling defect where blood flow is occluded. This direct imaging provides high sensitivity and specificity, allowing a clear and rapid diagnosis that guides immediate treatment decisions such as anticoagulation or thrombolysis.

D-dimer, while very sensitive, is not specific and cannot confirm PE on its own; a positive result suggests suspicion but requires imaging, and a negative result can rule out PE only in patients with low pretest probability. A V/Q scan can detect perfusion defects but often yields nondiagnostic results, especially in certain lung conditions, and is less definitive than CT angiography. Chest X-ray is not diagnostic for PE and usually only helps rule out other causes.