Which test differentiates pulmonary embolism?

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

Answer: (D)

When suspicion for pulmonary embolism exists, the goal is to confirm a clot inside the pulmonary arteries with an imaging test that directly visualizes the blockage. CT pulmonary angiography does this by using contrast-enhanced CT to image the pulmonary vessels and reveal filling defects where emboli are obstructing flow. This direct visualization provides a highly accurate diagnosis and helps guide treatment, making it the preferred test in most settings.

D-dimer is useful for ruling out PE in patients with low pretest probability because it’s very sensitive, but it’s not specific to PE—many conditions can raise D-dimer—so a positive result doesn’t confirm PE and a negative result isn’t definitive if the clinical suspicion is high. Chest X-ray is not diagnostic for PE; it’s often normal or shows non-specific findings and can’t confirm emboli. A V/Q scan can indicate a perfusion defect consistent with PE, but interpretation can be inconclusive or nondiagnostic in a sizable minority of patients, and CT angiography generally provides a clearer, more definitive diagnosis in contemporary practice.

So, the test that best differentiates pulmonary embolism is CT pulmonary angiography.