How do you assess the likelihood of pulmonary embolism?

Assessment of Pulmonary Embolism Likelihood

The most effective approach to assess pulmonary embolism likelihood is to use validated clinical prediction rules, particularly the Wells score, which demonstrates superior discriminative ability compared to other scales with an area under the curve of 0.85. 1

Clinical Prediction Rules

Wells Score

The Wells score is the most widely used and extensively validated clinical prediction tool for PE assessment. It categorizes patients into:

• Low risk (~10% PE prevalence): Wells score <2
• Moderate risk (~30% PE prevalence): Wells score 2-6
• High risk (~65-93% PE prevalence): Wells score >6 1, 2

The Wells score can also be used in a dichotomized form:

• PE unlikely: Score ≤4
• PE likely: Score >4 2

Wells score components include:

• Clinical signs of DVT (3 points)
• Alternative diagnosis less likely than PE (3 points)
• Heart rate >100 beats/min (1.5 points)
• Immobilization or surgery in previous 4 weeks (1.5 points)
• Previous DVT/PE (1.5 points)
• Hemoptysis (1 point)
• Malignancy (1 point) 2

Revised Geneva Score

An alternative validated tool that is fully standardized and does not include subjective elements:

• Age >65 years (1 point)
• Previous DVT or PE (3 points)
• Surgery or fracture within 1 month (2 points)
• Active malignancy (2 points)
• Unilateral lower limb pain (3 points)
• Hemoptysis (2 points)
• Heart rate 75-94 beats/min (3 points)
• Heart rate ≥95 beats/min (5 points)
• Pain on deep vein palpation and unilateral edema (4 points) 2

Clinician Gestalt

Clinical gestalt assessment is an unstructured estimate based on the clinician's training and experience. Studies show that experienced clinicians' gestalt has similar accuracy to structured decision tools 2, 3. However, structured tools provide more standardized assessment, especially for less experienced clinicians.

Risk Assessment Algorithm

1. Initial Assessment: Apply a validated clinical prediction rule (preferably Wells score) or use clinical gestalt to categorize PE risk 2, 1

2. For Low-Risk Patients (Wells score <2):

   • Apply PERC (Pulmonary Embolism Rule-Out Criteria) 2
   • If PERC negative (meets all 8 criteria), no further testing needed
   • If PERC positive, proceed to D-dimer testing

3. For Intermediate-Risk Patients (Wells score 2-6):

   • Proceed directly to D-dimer testing
   • Consider age-adjusted D-dimer cutoff for patients >50 years (age × 10 ng/mL) 2

4. For High-Risk Patients (Wells score >6):

   • Proceed directly to imaging (CTPA)
   • Do not perform D-dimer testing 2

Important Considerations

• PERC Criteria: Only apply to patients already assessed as low-risk. All criteria must be met to rule out PE without further testing:

  • Age <50 years
  • Heart rate <100 beats/min
  • Oxygen saturation ≥95%
  • No unilateral leg swelling
  • No hemoptysis
  • No recent trauma or surgery
  • No history of VTE
  • No hormone use 2

• D-dimer Testing: Highly sensitive but not specific. False positives are common in elderly patients, pregnant women, postoperative patients, and those with cancer or inflammatory conditions 2

• Imaging Decisions: The negative predictive value of CT pulmonary angiography varies with pretest probability:

  • Low pretest probability: 96% negative predictive value
  • Moderate pretest probability: 89% negative predictive value
  • High pretest probability: only 60% negative predictive value 2

Common Pitfalls to Avoid

1. Skipping pretest probability assessment: This can lead to unnecessary testing or missed diagnoses 2

2. Using D-dimer as a screening tool in patients without clinical suspicion of PE 1

3. Relying solely on negative CT results in high-risk patients without considering additional testing 2

4. Failing to use age-adjusted D-dimer cutoffs in older patients, leading to excessive imaging 2

5. Misapplying PERC criteria to patients who aren't already stratified as low-risk 2

By following this structured approach to PE likelihood assessment, clinicians can optimize diagnostic accuracy while minimizing unnecessary testing and radiation exposure.