Should I rule out Pulmonary Embolism (PE)?

Pulmonary Embolism Diagnostic Approach

Yes, you should rule out pulmonary embolism (PE) using a structured diagnostic algorithm based on clinical probability assessment, D-dimer testing, and appropriate imaging studies. 1

Diagnostic Algorithm for Suspected PE

Step 1: Assess Clinical Probability

First, use validated clinical prediction rules to estimate pretest probability of PE:

• Wells score or revised Geneva score
• Categorize patients as low, intermediate, or high probability (or PE-likely vs PE-unlikely)

Step 2: D-dimer Testing

• For low clinical probability patients:

  • If all PERC (Pulmonary Embolism Rule-Out Criteria) criteria are met, no further testing is needed 1
  • If PERC criteria not met, obtain high-sensitivity D-dimer test

• For intermediate clinical probability patients:

  • Obtain high-sensitivity D-dimer test
  • Use age-adjusted D-dimer cutoff (age × 10 ng/mL) for patients >50 years 1
  • Alternative approach: Use YEARS model-adjusted D-dimer levels (PE excluded in patients without clinical items and D-dimer <1000 mg/L, or with ≥1 clinical items and D-dimer <500 mg/L) 1

• For high clinical probability patients:

  • Skip D-dimer testing and proceed directly to imaging 1
  • D-dimer measurement is not recommended as even a normal result doesn't safely exclude PE in high-risk patients 1

Step 3: Imaging Studies

• If D-dimer is negative:

  • No further testing needed - PE is excluded 1

• If D-dimer is positive or in high clinical probability patients:

  • CT Pulmonary Angiography (CTPA) is the first-line imaging test 1
  • Ventilation-perfusion (V/Q) scan if CTPA is contraindicated (contrast allergy, renal dysfunction) 1
  • Lower-limb compression ultrasonography (CUS) can be considered in specific situations 1

Interpretation of Results

• Normal CTPA:

  • In low/intermediate probability: Safely excludes PE without further testing 1
  • In high probability: Consider additional testing as PE cannot be completely ruled out 1

• Positive CTPA (segmental or more proximal filling defect):

  • In intermediate/high probability: Confirms PE diagnosis without further testing 1

• Isolated subsegmental filling defects:

  • Consider further imaging tests to confirm PE 1

• V/Q scan:

  • Normal perfusion scan: Excludes PE 1
  • High probability V/Q scan: Confirms PE 1
  • Non-diagnostic V/Q scan + negative proximal CUS + low clinical probability: Excludes PE 1

Important Caveats and Pitfalls

1. D-dimer limitations:

   • Less useful in hospitalized patients, elderly, and those with comorbidities due to lower specificity 1
   • Higher D-dimer levels (>2.0 mg/L) are strongly associated with PE 2
   • Very high D-dimer levels (>6.0 mg/L) may indicate more severe PE with hemodynamic compromise 2

2. Clinical presentation variability:

   • Symptoms can be vague, especially in older patients where fatigue may be the only symptom 2
   • Classic symptoms like pleuritic pain are more common in younger patients 2

3. Mortality risk:

   • Untreated PE has approximately 30% mortality rate, while treated PE has <8% mortality 3
   • Prompt diagnosis and treatment significantly improve outcomes

4. Diagnostic challenges:

   • No single non-invasive test is both highly sensitive and specific 4
   • Combination of clinical assessment and appropriate testing is essential

By following this structured approach, you can effectively rule out PE in low-risk patients while ensuring appropriate diagnosis and treatment in those with higher probability of disease, ultimately reducing morbidity and mortality.