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?

Compression Ultrasound Following Positive D-dimer Without Additional Imaging

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

Diagnostic Algorithm Based on Clinical Probability

Low Clinical Probability Patients

• For patients with low clinical probability (Wells score <2):
  • A positive D-dimer followed by a negative initial proximal compression ultrasound requires either:
    • Repeat proximal ultrasound in 1 week OR
    • Whole-leg ultrasound 1
  • Stopping after a single negative proximal ultrasound with positive D-dimer fails to meet established safety thresholds 1

Intermediate/High Clinical Probability Patients

• For patients with intermediate/high clinical probability (Wells score ≥2):
  • A negative initial proximal ultrasound requires additional testing regardless of D-dimer status
  • Options include:
    • Serial proximal ultrasound (repeat in 1 week)
    • Whole-leg ultrasound
    • Venography in select cases 1
  • The American Society of Hematology specifically recommends against using a positive D-dimer alone to diagnose DVT in intermediate probability patients 1

Special Considerations

When a Single Ultrasound May Be Sufficient

• A negative whole-leg ultrasound (examining both proximal and distal veins) may not require follow-up imaging, even with a positive D-dimer 1, 2
• However, this approach is only recommended when:
  1. The whole-leg ultrasound is performed by experienced technicians
  2. The quality of imaging is optimal
  3. There are no technical limitations 1

High-Risk Scenarios Requiring Additional Testing

• Cancer patients have higher false-positive D-dimer rates and higher DVT risk 3
• Patients with extensive unexplained leg swelling should have iliac veins imaged even with negative proximal ultrasound 1, 3
• Patients with severe symptoms consistent with calf DVT should undergo whole-leg ultrasound rather than proximal-only 1

Diagnostic Accuracy Considerations

• D-dimer has a negative predictive value of 96% for isolated distal DVT, but its sensitivity is only 84% 4
• In patients with low pretest probability, D-dimer negative predictive value increases to 99% for isolated distal DVT 4
• For proximal DVT, the combination of negative D-dimer and negative ultrasound has a negative predictive value of 98-99% 5

Common Pitfalls to Avoid

1. Relying solely on D-dimer: D-dimer should never be used as a stand-alone test to diagnose DVT, particularly in high-risk patients 1
2. Stopping after 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 and negative proximal ultrasound, iliac vein imaging is necessary to exclude isolated iliac DVT 1, 3
4. Overlooking alternative diagnoses: When DVT is ruled out, alternative diagnoses should be pursued, especially when symptoms persist 1

In conclusion, while a simplified approach using D-dimer followed by a single whole-leg ultrasound has been studied 2, the established guidelines from the American College of Chest Physicians and American Society of Hematology still recommend follow-up imaging after a negative proximal ultrasound in patients with positive D-dimer to ensure patient safety and minimize the risk of missed DVT 1.