Why is a d-dimer (Deep Vein Thrombosis/Pulmonary Embolism marker) test checked?

Why Check a D-dimer Test

D-dimer testing is primarily valuable as a rule-out test for venous thromboembolism (VTE) in patients with low to intermediate clinical probability, with a negative result safely excluding VTE when combined with appropriate clinical assessment. 1

Role of D-dimer in VTE Diagnosis

D-dimer is a specific breakdown product of cross-linked fibrin that serves as a sensitive marker for acute thrombosis. When used appropriately, it plays a crucial role in the diagnostic algorithm for suspected pulmonary embolism (PE) and deep vein thrombosis (DVT).

Key Characteristics of D-dimer Testing:

• High sensitivity (93-96%) but poor specificity (39-51%) for VTE 1
• A negative D-dimer combined with low/intermediate clinical probability safely excludes VTE with a 3-month thromboembolic risk of less than 1% 1
• The HemosIL HS D-dimer has demonstrated 96.0% sensitivity with a negative post-test probability of only 0.3% 2

When to Use D-dimer Testing

D-dimer testing is most appropriate in:

• Outpatient settings where disease prevalence and comorbidities are lower 3
• Patients with low to intermediate clinical probability of VTE 1
• As part of a sequential diagnostic strategy that includes clinical probability assessment 1

When NOT to Use D-dimer Testing

D-dimer should not be used:

• In patients with high clinical probability of VTE (proceed directly to imaging) 1
• As a standalone test to rule in VTE due to poor specificity 1
• As the primary diagnostic tool in certain populations where specificity is extremely poor:
  • Hospitalized patients
  • Pregnant patients (specificity as low as 6-23%)
  • Cancer patients (specificity as low as 18-21%)
  • Elderly patients without age adjustment
  • Post-surgical patients
  • Patients with inflammatory conditions 1

Diagnostic Algorithm Using D-dimer

1. First step: Assess clinical probability using validated tools like Wells criteria 1
2. Second step: Order D-dimer test based on clinical probability:
   • For low/intermediate probability: Perform D-dimer test
   • For high probability: Skip D-dimer and proceed directly to imaging 1
3. Third step: Interpret results:
   • Negative D-dimer + low/intermediate probability: VTE ruled out (no further testing)
   • Positive D-dimer: Proceed to imaging (CTPA for PE, ultrasound for DVT)
   • For patients over 50 years: Use age-adjusted D-dimer cutoff (age × 10 μg/L) 1

Common Pitfalls and Caveats

• False positives are common due to poor specificity, especially in hospitalized patients, pregnancy, cancer, elderly, post-surgical patients, and inflammatory conditions 1
• Test characteristics vary significantly between different D-dimer assays - results from one manufacturer's test may not apply to others 3
• Traditional latex and whole agglutination tests have lower sensitivity and should not be used to rule out PE 4
• In elderly patients, specificity decreases significantly with age - use age-adjusted cutoffs for patients over 50 1
• A normal D-dimer cannot safely rule out PE in pregnant patients due to extremely poor specificity 1

Clinical Context

The American College of Radiology notes that D-dimer testing has evolved as part of the diagnostic approach for suspected PE, with high-sensitivity D-dimer testing using enzyme-linked immunosorbent assay improving the specificity of PE diagnosis. A negative D-dimer test effectively excludes PE or DVT in appropriate clinical scenarios, though it has limited value in pregnant, postoperative, trauma patients, and those determined to be at high risk of PE by validated clinical criteria. 4