What are the Pulmonary Embolism Rule-out Criteria (PERC) for diagnosing pulmonary embolism?

Pulmonary Embolism Rule-out Criteria (PERC)

The Pulmonary Embolism Rule-out Criteria (PERC) is a validated clinical decision tool that can safely rule out pulmonary embolism without further testing in patients with low pretest probability, avoiding unnecessary testing and potential harm when all eight criteria are met. 1

PERC Criteria Components

The PERC rule consists of 8 objective criteria that must all be negative to safely rule out PE:

• Age < 50 years 1
• Heart rate < 100 beats per minute 1
• Oxygen saturation ≥ 95% on room air 1
• No unilateral leg swelling 1
• No hemoptysis 1
• No recent trauma or surgery (within 4 weeks) 1
• No prior history of venous thromboembolism (VTE) 1
• No hormone use (estrogen-containing oral contraceptives or hormone replacement therapy) 1

Proper Application of PERC

PERC should be applied only in specific clinical scenarios:

• Only in patients with low pretest probability of PE (based on clinical gestalt or a validated clinical decision tool) 1
• PERC is not a screening tool for all patients with respiratory symptoms 1
• PERC should only be applied to patients in whom a clinician has a genuine concern about PE 1

Clinical Performance and Safety

• Meta-analysis data shows PERC has a sensitivity of 97% (95% CI, 96% to 98%) and specificity of 22% (CI, 22% to 23%) 1
• When properly applied, PERC has a very low miss rate of only 0.3% (44 of 14,844 cases) 1
• Using PERC could safely avoid approximately 22% of d-dimer tests in appropriate patients 1

Diagnostic Algorithm for Suspected PE

1. First step: Assess pretest probability using clinical gestalt or validated tools 1

2. For low pretest probability patients:

   • Apply PERC rule
   • If all PERC criteria negative (PERC-): No further testing needed 1
   • If any PERC criteria positive (PERC+): Proceed to d-dimer testing 1

3. For intermediate pretest probability patients:

   • D-dimer testing is warranted (PERC not applicable) 1
   • Normal d-dimer (ideally age-adjusted for patients >50 years): No further imaging needed 1
   • Elevated d-dimer: Proceed to imaging 1

4. For high pretest probability patients:

   • Proceed directly to imaging (PERC not applicable) 1
   • D-dimer testing should not be performed 1
   • CTPA is preferred imaging method when available and not contraindicated 1

Common Pitfalls and Caveats

• PERC should not be used as a general screening tool for all patients with respiratory symptoms 1
• PERC should only be applied to patients already determined to have low pretest probability 1
• Some European studies suggest caution in populations with high PE prevalence 2, 3
• More recent European data supports PERC use in low clinical probability patients with a false-negative rate of only 1.2% (95% CI 0.4-2.9%) 4
• Applying PERC to intermediate or high-risk patients may lead to missed diagnoses 1
• Current practice often does not follow guidelines, with many low-risk patients undergoing unnecessary imaging 1

Impact on Clinical Practice

• When properly implemented, PERC can reduce unnecessary testing, radiation exposure, and healthcare costs 5
• Studies show PERC could safely avoid 11.5% of CT angiograms in appropriate populations 5
• The combination of PERC with clinical gestalt appears particularly effective for safely excluding PE 3

By following this evidence-based approach to PE diagnosis using PERC in appropriate low-risk patients, clinicians can reduce unnecessary testing while maintaining patient safety and improving healthcare resource utilization.