Is it acceptable to order a compression ultrasound (US) of the lower extremities to evaluate for deep vein thrombosis (DVT) in a patient with a positive D-dimer without ordering any follow-up imaging?

Diagnostic Approach for DVT in Patients with Positive D-dimer

A single negative compression ultrasound of the lower extremities is insufficient to rule out DVT in patients with a positive D-dimer, and follow-up imaging is required in most clinical scenarios. 1

Diagnostic Algorithm Based on Clinical Probability

For Patients with Low Clinical Probability (Wells score <2)

• Initial positive D-dimer requires compression ultrasound (CUS) of proximal veins
• If initial proximal CUS is negative:
  • Repeat proximal CUS in 1 week OR
  • Perform whole-leg ultrasound 2, 1
• Stopping after a single negative proximal ultrasound with positive D-dimer misses 1-2% of DVTs that could extend proximally 1

For Patients with Moderate Clinical Probability (Wells score 2-6)

• Initial positive D-dimer requires proximal CUS or whole-leg US
• If proximal CUS is negative:
  • Repeat proximal CUS in 1 week OR
  • Perform D-dimer testing (if not already done) 2
• If proximal CUS is negative but D-dimer is positive:
  • Repeat proximal CUS in 1 week is required 2

For Patients with High Clinical Probability (Wells score >6)

• Proceed directly to proximal CUS or whole-leg US
• If initial proximal CUS is negative:
  • Repeat proximal CUS in 1 week OR
  • Perform venographic-based imaging 2

Special Considerations

Whole-Leg Ultrasound

• If whole-leg US is performed and negative, no further testing is needed, even with a positive D-dimer 2, 3
• Whole-leg US is preferred for:
  • Patients unable to return for serial testing
  • Those with severe symptoms consistent with calf DVT 2
  • Patients with extensive unexplained leg swelling (should include iliac vein imaging) 1

Diagnostic Accuracy

• Duplex and triplex ultrasound techniques have higher sensitivity (96.5% and 96.4% respectively) for proximal DVT compared to compression US alone (93.8%) 4
• Specificity remains high across all techniques (93.8-97.8%) 4

Common Pitfalls to Avoid

1. Relying solely on D-dimer: D-dimer should never be used as a stand-alone test to diagnose DVT 1

2. Stopping after a single negative proximal ultrasound with positive D-dimer: This approach misses 1-2% of DVTs that could extend proximally 1

3. Failing to image iliac veins in patients with extensive unexplained swelling: Can lead to missed diagnoses of isolated iliac DVT 1

4. Not considering alternative diagnoses: When initial testing is negative but clinical suspicion remains high, consider alternative diagnoses

5. Overreliance on standard D-dimer cutoffs: Some studies suggest higher D-dimer cutoffs (e.g., >1251 ng/ml FEU) might be more appropriate in certain populations 5

In conclusion, for patients with a positive D-dimer, a single negative compression ultrasound is insufficient to exclude DVT in most clinical scenarios. The appropriate follow-up testing depends on clinical probability assessment, with repeat ultrasound or whole-leg ultrasound being the most commonly recommended approaches.