What diagnostic test is most definitive for suspected pulmonary embolism?

• A. D-dimer assay
• B. CT pulmonary angiography (CTPA)
• C. V/Q scan
• D. Chest radiograph

Answer: (B)

When evaluating suspected pulmonary embolism, the test that most definitively confirms the diagnosis is CT pulmonary angiography. This imaging modality uses contrast to directly visualize the pulmonary arteries, allowing you to see the presence, size, and exact location of an embolus. It provides rapid, highly accurate information about the clot and can also reveal any secondary lung effects or alternative diagnoses, making it the gold standard for confirmation when no contraindications exist.

D-dimer is very sensitive and good for ruling out PE in patients with low pretest probability, but it’s not specific—many other conditions can raise D-dimer—so a positive result can’t confirm PE by itself. A ventilation-perfusion (V/Q) scan can identify mismatches in ventilation and perfusion, but it can be nondiagnostic or inconclusive in many patients, limiting its definitiveness. Chest radiographs are non-specific and typically do not diagnose PE, though they help assess alternative causes.

So, CT pulmonary angiography stands out as the most definitive test for confirming suspected pulmonary embolism.