Question

In a patient with a high clinical suspicion of pulmonary thromboembolism, which is the best investigation?

• A. D-dimer
• B. CT angiography
• C. Catheter angiography
• D. Colour Doppler

Hint:

High suspicion needs a confirmatory test - CT pulmonary angiography, not D-dimer.

Answer 1

The Correct Option is B

Step 1: Choosing the test depends on pre-test probability. When clinical suspicion of pulmonary embolism (PE) is high, the aim is a definitive imaging test that can confirm the clot, not a screening test.

Step 2: D-dimer is a sensitive but non-specific screening test. It is useful to rule out PE when suspicion is low, but with high clinical suspicion a normal or abnormal D-dimer does not change management, so it is not the best choice here.

Step 3: CT pulmonary angiography (spiral or helical CT with intravenous contrast) is the principal imaging test for diagnosing PE. It visualises up to sixth-order branches, detects small peripheral emboli, and also assesses right ventricular size for risk stratification. It is non-invasive and is the investigation of choice.

Step 4: Conventional catheter pulmonary angiography is the historical gold standard but is invasive and has been largely replaced by CT. Colour Doppler images the leg veins, not the pulmonary arteries directly. Hence CT angiography is the best answer.