What is the clinical significance of D-dimer testing in suspected PE or DVT?

• A. It has high sensitivity but low specificity; a negative D-dimer can help rule out PE/DVT in low-risk patients.
• B. It has high specificity but low sensitivity; a positive D-dimer confirms PE/DVT.
• C. It directly visualizes clots in pulmonary arteries.
• D. It is not useful in evaluating suspected thromboembolism.

Answer: (B)

D-dimer testing is most useful for ruling out thromboembolism rather than confirming it. The test is very sensitive for clot formation and breakdown, so a negative result strongly argues against a PE or DVT in patients who are low risk. This gives a high negative predictive value, meaning you can often avoid imaging in those low‑probability cases.

However, D-dimer has low specificity. Many non-thrombotic factors—such as infection, inflammation, cancer, recent surgery, age, or pregnancy—can raise D-dimer levels. Because of that, a positive result does not confirm PE or DVT; it simply raises suspicion and usually leads to imaging to establish a diagnosis.

In practice, you combine pretest probability with D-dimer results: if risk is low and the D-dimer is negative, you can rule out clot. If risk is intermediate or high, or if the D-dimer is positive, you proceed to definitive imaging (like CT pulmonary angiography for PE or compression ultrasound for DVT). Age-adjusted thresholds can help improve specificity in older patients.