Does an elevated D-dimer (D-dimer) level above the age-adjusted threshold require a computed tomography pulmonary angiography (CTPA) to rule out pulmonary embolism, even with low clinical suspicion?

Elevated D-dimer Alone Does Not Require CTPA Without Clinical Suspicion

An elevated D-dimer above the age-adjusted threshold does not automatically require CTPA when there is no clinical suspicion of pulmonary embolism. Clinical probability assessment must precede and guide the interpretation of D-dimer results in the diagnostic algorithm for PE.

Diagnostic Algorithm for Suspected PE

Step 1: Clinical Probability Assessment

• Always begin with assessment of clinical probability using validated tools like Wells score or Geneva score, or clinician gestalt 1
• Clinical probability stratification is the essential first step that determines subsequent testing strategy 1

Step 2: D-dimer Testing Based on Clinical Probability

• Low clinical probability:

  • If patient meets all PERC criteria (Pulmonary Embolism Rule-Out Criteria), no D-dimer testing or imaging is needed 1
  • If patient does not meet all PERC criteria, obtain high-sensitivity D-dimer 1

• Intermediate clinical probability:

  • Obtain high-sensitivity D-dimer measurement as initial diagnostic test 1
  • Do not proceed directly to imaging studies 1

• High clinical probability:

  • Proceed directly to CTPA without D-dimer testing 1
  • D-dimer testing is not recommended in high probability cases as a negative result does not safely exclude PE 1

Step 3: Interpretation of D-dimer Results

• For patients >50 years old, use age-adjusted D-dimer thresholds (age × 10 ng/mL) rather than fixed 500 ng/mL cutoff 1
• If D-dimer is below the appropriate threshold (standard or age-adjusted), PE can be safely excluded without imaging 1
• If D-dimer is elevated above the threshold, proceed to CTPA 1

Important Considerations

• D-dimer has high negative predictive value but poor positive predictive value for PE 1

• D-dimer levels are frequently elevated in other conditions including:

  • Cancer 1
  • Hospitalized patients 1
  • Severe infection or inflammatory disease 1
  • Pregnancy 1
  • Advanced age 1

• The specificity of D-dimer decreases steadily with age, dropping to only 10% in patients >80 years 1, 2

Common Pitfalls to Avoid

• Ordering D-dimer without clinical assessment: Clinical probability must be determined first 1
• Proceeding directly to CTPA with elevated D-dimer but low clinical suspicion: This leads to unnecessary radiation exposure and contrast risks 1
• Ignoring clinical assessment when D-dimer is elevated: D-dimer elevation alone is not diagnostic of PE 1
• Ordering D-dimer in high probability patients: This is not recommended as imaging is required regardless of D-dimer result 1
• Using standard D-dimer cutoff for elderly patients: Age-adjusted thresholds improve specificity without reducing sensitivity 1, 2

Conclusion

The colleague who did not order D-dimer testing was following appropriate practice if clinical suspicion was low and PERC criteria were met, or if clinical suspicion was high (where D-dimer is not recommended). An elevated D-dimer in isolation does not mandate CTPA without considering the clinical context and pretest probability of PE 1.