What is the role of the D-dimer (D-dimer) test in diagnosing deep vein thrombosis (DVT) or pulmonary embolism (PE)?

Role of D-dimer Testing in Diagnosing DVT and PE

D-dimer testing is primarily valuable as a rule-out test for venous thromboembolism (VTE) in patients with low to intermediate clinical probability, but should not be used in patients with high clinical probability as it cannot safely exclude PE in this population. 1, 2

Clinical Probability Assessment First

• Always begin with clinical probability assessment using validated tools:
  • Wells criteria for DVT/PE
  • Revised Geneva score for PE
  • These stratify patients into low, moderate, or high probability categories 2

D-dimer Testing Algorithm

Clinical Probability	D-dimer Result	Next Step
Low	Negative	VTE ruled out (no further testing needed)
Low	Positive	Proceed to imaging (ultrasound for DVT, CTPA for PE)
Intermediate	Negative	VTE ruled out (no further testing needed)
Intermediate	Positive	Proceed to imaging
High	Not recommended	Proceed directly to imaging regardless of D-dimer

Key Characteristics of D-dimer Testing

• Sensitivity: Excellent (93-96%) - makes it valuable for excluding VTE
• Specificity: Poor (39-51%) - leads to many false positives 2
• Negative Predictive Value: Very high (>99%) in low/intermediate probability patients 3

Important Limitations

D-dimer testing has reduced utility in:

1. Hospitalized patients: High frequency of positive results with standard thresholds 2
2. Elderly patients: Specificity decreases significantly with age
   • Use age-adjusted cut-offs (age × 10 ng/mL) for patients over 50 years 1, 2
3. Pregnant patients: Very poor specificity (as low as 6-23%) 2
4. Cancer patients: Significantly reduced specificity (18-21%) 2
5. Post-surgical patients: Elevated due to surgical trauma 2
6. Inflammatory conditions: Non-specific elevation 2

Special Considerations

• For hemodynamically unstable patients with suspected PE:

  • Bedside echocardiography should be used to assess for RV dysfunction
  • If RV dysfunction is present, consider immediate reperfusion therapy
  • Confirm diagnosis with CTPA once stabilized 2

• For suspected PE with low/intermediate probability:

  • Negative D-dimer safely excludes PE (3-month thromboembolic risk <1%) 1
  • Positive D-dimer requires CTPA for confirmation 1

• Finding a proximal DVT on ultrasound in a patient with suspected PE is sufficient to warrant anticoagulation without further testing 1, 2

Common Pitfalls to Avoid

1. Do not use D-dimer in high clinical probability patients - A normal result does not safely exclude PE in this population 1

2. Do not rely on D-dimer alone - Always combine with clinical probability assessment 2

3. Do not dismiss positive D-dimer results in low-risk patients without confirmatory imaging 2

4. Do not use standard cut-offs in elderly patients - Use age-adjusted thresholds 1, 2

5. Be cautious with D-dimer interpretation after 48 hours of hospitalization - Specificity decreases significantly 2