What is the diagnostic algorithm for Pulmonary Embolism (PE)?

Diagnostic Algorithm for Pulmonary Embolism

The diagnostic approach for pulmonary embolism should follow a structured algorithm based on hemodynamic status, clinical probability assessment, D-dimer testing, and appropriate imaging, with CT pulmonary angiography being the first-line imaging test for most patients. 1, 2

Initial Assessment: Hemodynamic Status

The first step in the diagnostic algorithm is to determine the patient's hemodynamic status:

For Patients with Hemodynamic Instability (High-Risk PE Suspected):

1. Bedside transthoracic echocardiography (TTE) should be performed immediately 1

   • If TTE shows right ventricular (RV) dysfunction without other obvious cause, consider PE likely
   • In critically unstable patients, echocardiographic evidence of RV dysfunction is sufficient to prompt immediate reperfusion without further testing

2. If CT is immediately available and patient can be transported safely:

   • Proceed to CT pulmonary angiography (CTPA)
   • If CTPA confirms PE, initiate appropriate treatment
   • If CTPA is negative, search for alternative causes of shock

3. If CT is not immediately available or patient cannot be transported:

   • Consider additional bedside tests:
     • Transoesophageal echocardiography (TOE) to visualize thrombi in pulmonary arteries
     • Compression ultrasonography (CUS) to detect DVT, which would support PE diagnosis

![Diagnostic algorithm for suspected high-risk PE with hemodynamic instability]

For Hemodynamically Stable Patients (Non-High-Risk PE Suspected):

Step 1: Clinical Probability Assessment

Use validated clinical prediction rules to assess pre-test probability:

• Wells Score or Revised Geneva Score 1, 2
• Can be used as three-level (low/intermediate/high) or two-level (PE-unlikely/PE-likely) classification

Revised Geneva Score components:

• Previous PE or DVT: 3 points (original) or 1 point (simplified)
• Heart rate 75-94 bpm: 3 points (original) or 1 point (simplified)
• Heart rate ≥95 bpm: 5 points (original) or 2 points (simplified)
• Surgery or fracture within past month: 2 points (original) or 1 point (simplified)
• Hemoptysis: 2 points (original) or 1 point (simplified)
• Active cancer: 2 points (original) or 1 point (simplified)
• Unilateral lower-limb pain: 3 points (original) or 1 point (simplified)
• Pain on lower-limb deep venous palpation and unilateral edema: 4 points (original) or 1 point (simplified)
• Age >65 years: 1 point (both versions)

Step 2: D-dimer Testing

• For low or intermediate clinical probability (or PE-unlikely):

  • Perform D-dimer testing
  • Use age-adjusted D-dimer cutoff for patients >50 years (age × 10 ng/mL) to improve specificity 1, 2
  • If D-dimer is negative, PE can be safely excluded (3-month thromboembolic risk <1%) 1
  • If D-dimer is positive, proceed to imaging

• For high clinical probability (or PE-likely):

  • D-dimer testing is not recommended due to low negative predictive value
  • Proceed directly to imaging 1

• Alternative D-dimer approach (YEARS algorithm): 1

  • For patients with no YEARS items (signs of DVT, hemoptysis, PE most likely diagnosis): PE excluded if D-dimer <1000 ng/mL
  • For patients with ≥1 YEARS item: PE excluded if D-dimer <500 ng/mL

Step 3: Imaging

• First-line imaging: CT Pulmonary Angiography (CTPA) 1

  • Allows visualization of pulmonary arteries down to subsegmental level
  • Sensitivity 83%, specificity 96%
  • A negative CTPA adequately excludes PE in patients with low/intermediate clinical probability
  • If CTPA positive, treat for PE

• When CTPA is contraindicated or unavailable:

  • Ventilation/perfusion (V/Q) lung scintigraphy or V/Q SPECT
  • Lower limb compression ultrasonography (CUS) to detect DVT

• Special considerations:

  • For patients with high clinical probability and negative CTPA, consider further testing
  • For pregnant patients, both CTPA and V/Q scan can be used safely with appropriate protocols 2

![Diagnostic algorithm for suspected PE without hemodynamic instability]

Common Pitfalls to Avoid

1. Failing to assess clinical probability before ordering tests, which should guide the diagnostic approach 1

2. Inappropriate use of D-dimer testing:

   • Using D-dimer in high clinical probability patients
   • Not using age-adjusted cutoffs in elderly patients
   • Relying on point-of-care D-dimer tests which have lower sensitivity (88% vs. 95% for laboratory tests) 1

3. Misinterpreting single subsegmental PE on CTPA, which may be a false positive 2

4. Delaying anticoagulation in patients with high clinical probability while awaiting confirmatory tests 2

5. Overreliance on clinical signs and symptoms alone, which are often nonspecific (chest pain, dyspnea, tachycardia) 1

6. Misinterpreting normal oxygen saturation as ruling out PE (up to 40% of PE patients have normal SaO2) 1

7. Not considering PE in pregnant patients due to concern about radiation exposure 2

By following this structured diagnostic algorithm, clinicians can effectively diagnose or exclude PE while minimizing unnecessary testing and treatment delays that could impact patient mortality and morbidity.