What is the role of Pulmonary Embolism Rule-out Criteria (PERC) in diagnosing and managing pulmonary embolism (PE)?

Role of Pulmonary Embolism Rule-out Criteria (PERC) in PE Management

The PERC rule should be used to safely exclude pulmonary embolism in patients with low clinical probability without requiring additional diagnostic testing, potentially reducing unnecessary imaging studies by up to 23%. 1

What is the PERC Rule?

The PERC rule is a validated clinical decision tool consisting of 8 criteria that must all be negative to safely rule out PE without further testing:

• Age < 50 years
• Heart rate < 100 beats/minute
• Oxygen saturation ≥ 95% (at sea level)
• No history of venous thromboembolism
• No recent trauma or surgery
• No hemoptysis
• No estrogen use
• No unilateral leg swelling 2, 1

Diagnostic Algorithm Using PERC

1. First Step: Assess clinical probability using validated tools (Wells score or Geneva score) or clinical gestalt
2. For Low-Risk Patients:
   • Apply PERC rule
   • If PERC negative (all criteria met): No further testing needed, PE can be safely ruled out
   • If PERC positive (any criteria not met): Proceed to D-dimer testing 1
3. For Intermediate-Risk Patients:
   • PERC rule not applicable
   • Proceed directly to D-dimer testing
   • If D-dimer negative: PE excluded
   • If D-dimer positive: Proceed to imaging (CTPA) 1
4. For High-Risk Patients:
   • PERC rule not applicable
   • Proceed directly to imaging (CTPA) without D-dimer testing 1

Evidence Supporting PERC

The American College of Emergency Physicians (ACEP) provides a Level B recommendation for using PERC in patients with low pretest probability to exclude PE based on historical and physical examination data alone 2. When properly applied, PERC has demonstrated high sensitivity and negative predictive value in multiple studies.

A retrospective study in a community hospital showed that PERC had 100% sensitivity (95% CI, 78.12-100%) and 100% negative predictive value (95% CI, 90.80-100%) for ruling out PE. Application of PERC at the point-of-care would have reduced CT scans by 23% 3.

Similarly, another study found that PERC had a sensitivity of 96.9% (95% CI, 84.3%-99.4%) and a negative predictive value of 98.8% (95% CI, 93.5%-99.8%) when used as an independent diagnostic test to exclude PE 4.

Important Caveats and Limitations

1. PERC is only valid in low-risk populations: The rule should only be applied to patients already deemed to have a low clinical probability of PE using validated clinical prediction rules or clinical gestalt 2, 1.

2. Prevalence matters: Some studies have challenged PERC's safety in high-prevalence populations. One study found a PE prevalence of 5.4% among PERC-negative patients overall, suggesting caution in populations with high PE prevalence 5.

3. Combining with clinical assessment: When PERC is combined with low clinical probability assessment, particularly using clinical gestalt rather than formal scoring systems, its performance may improve. One study found 0% PE prevalence when PERC was combined with low gestalt probability 6.

4. Do not apply PERC to intermediate or high-risk patients: PERC is specifically designed for low-risk patients and should not be used to rule out PE in patients with intermediate or high clinical probability 1.

5. Complete application: All eight criteria must be negative to safely rule out PE. If any single criterion is positive, proceed with standard diagnostic testing 1.

Clinical Impact

Proper application of the PERC rule can:

• Reduce unnecessary CT pulmonary angiography by 11.5-23% 3, 4
• Decrease radiation exposure to patients
• Reduce ED length of stay
• Lower healthcare costs
• Minimize adverse events from contrast exposure and unnecessary anticoagulation

By incorporating PERC into clinical practice for appropriate patients, clinicians can safely exclude PE without exposing patients to the risks of unnecessary diagnostic testing, while maintaining high diagnostic accuracy for this potentially fatal condition.