In suspected pulmonary embolism, which describes the role of D-dimer testing?

• A. D-dimer is used as a screening test; a positive result prompts imaging.
• B. D-dimer alone confirms PE.
• C. D-dimer is not useful in evaluating PE.
• D. D-dimer replaces the need for imaging when suspicion is high.

Answer: (A)

D-dimer testing is a highly sensitive, but nonspecific, screening tool for suspected PE. The main idea is to use it to rule out disease in patients with low to intermediate pretest probability. If the D-dimer is negative in this context, PE is unlikely and imaging can often be avoided. However, a positive D-dimer does not confirm PE because many conditions can raise D-dimer levels, so imaging—usually CT pulmonary angiography—is needed to make a definitive diagnosis. D-dimer by itself cannot confirm PE and cannot replace imaging when clinical suspicion remains high, but it is still useful as a rule-out test in the appropriate patients.