Which of the following is a test for DVT?

• A. Venography
• B. Duplex ultrasound
• C. D-dimer blood test
• D. Blood glucose

Answer: (C)

D-dimer testing is used in evaluating suspected DVT because it detects fragments formed when a blood clot is being broken down. The D-dimer is a byproduct of fibrin degradation, so its presence suggests that clotting has occurred somewhere in the body.

The reason this test is helpful is its high sensitivity. A negative D-dimer makes active DVT unlikely, especially in patients with low pretest probability, so it can effectively rule out DVT in those cases. However, a positive result doesn’t confirm a clot on its own, since D-dimer can be elevated for many reasons (recent surgery, infection, pregnancy, inflammation, etc.). In those situations, imaging—typically duplex ultrasound—would be used to confirm whether a DVT is actually present.

Other options aren’t direct tests for DVT in routine practice: venography is an invasive imaging test that used to be the reference standard but isn’t commonly used now; duplex ultrasound is the standard imaging test that visually confirms a thrombus; blood glucose is unrelated to DVT.