What is the clinical utility of D-dimer testing, and what does a negative test imply in a patient with low pretest probability for PE?

• A. A negative D-dimer excludes PE/DVT in all patients.
• B. D-dimer testing helps exclude PE/DVT in low-risk patients; a negative test makes PE unlikely.
• C. A positive D-dimer confirms PE.
• D. D-dimer testing replaces imaging in all cases.

Answer: (B)

The key idea is how D-dimer testing is used with initial clinical probability to rule out PE/DVT. D-dimer is a very sensitive marker of clot formation, but it’s not specific: many conditions can raise it. Because of that, its strongest value comes when you start with a population that’s low enough in likelihood that a negative result would meaningfully reduce the chance of disease.

In patients with low pretest probability for PE, a negative D-dimer has a high negative predictive value. That means PE becomes unlikely enough that you can often avoid imaging and still be confident in ruling out PE. A positive D-dimer, by contrast, does not confirm PE—it's nonspecific and would prompt further imaging to determine whether a clot is actually present.

So the best interpretation is that D-dimer testing helps exclude PE/DVT in low-risk patients; a negative result makes PE unlikely. It’s not a universal rule-out for everyone, and it does not replace imaging when suspicion remains or when pretest probability is high.