PERC Rule Instructions
The PERC (Pulmonary Embolism Rule-out Criteria) rule is used to identify patients with low probability of pulmonary embolism who may not require further testing. Select all criteria that apply to the patient. A score of 0 (PERC negative) suggests PE can be safely excluded in patients with low clinical suspicion.
Patient is 50 years of age or older
Heart rate is 100 beats per minute or higher
Pulse oximetry shows oxygen saturation below 95%
Swelling in one leg only
Coughing up blood
Surgery or trauma within the past 4 weeks
History of pulmonary embolism or deep vein thrombosis
Current use of estrogen-containing medications
PERC Rule Interpretation
- PERC Negative (0 criteria): Low probability of PE
- PERC Positive (≥1 criteria): Further evaluation needed
- PERC rule should only be used in patients with low clinical suspicion
- High clinical suspicion requires immediate evaluation regardless of PERC score
Clinical Pearls
- PERC rule has 96.4% sensitivity and 27.4% specificity
- False negative rate is approximately 1.0%
- Use only in patients with low clinical suspicion
- High suspicion patients need immediate evaluation
- Consider D-dimer testing for PERC positive patients
PERC Rule for Pulmonary Embolism
The PERC (Pulmonary Embolism Rule-out Criteria) rule is a validated clinical decision tool designed to identify patients with low probability of pulmonary embolism who may not require further diagnostic testing. This rule is particularly useful in emergency departments and outpatient settings to reduce unnecessary imaging and improve resource utilization.
PERC Rule Criteria
The PERC rule consists of 8 criteria, each assigned 1 point if present:
Where
- Age ≥ 50 years - Patient is 50 years of age or older
- Heart rate ≥ 100 bpm - Heart rate is 100 beats per minute or higher
- Oxygen saturation < 95% - Pulse oximetry shows oxygen saturation below 95%
- Unilateral leg swelling - Swelling in one leg only
- Hemoptysis - Coughing up blood
- Recent surgery or trauma - Surgery or trauma within the past 4 weeks
- Prior PE or DVT - History of pulmonary embolism or deep vein thrombosis
- Estrogen use - Current use of estrogen-containing medications
PERC Rule Interpretation
Clinical Decision Algorithm
Performance Characteristics
| Metric | Value | Clinical Significance |
|---|---|---|
| Sensitivity | 96.4% | Very high - misses few cases |
| Specificity | 27.4% | Low - many false positives |
| Negative Predictive Value | 99.1% | Excellent - very safe to exclude |
| False Negative Rate | 1.0% | Very low risk of missing PE |
Clinical Applications
Primary Use
- Emergency Department: Rapid assessment of low-risk patients
- Outpatient Settings: Evaluation of suspected PE in ambulatory care
- Resource Optimization: Reduce unnecessary imaging and costs
- Risk Stratification: Identify patients who need further testing
Integration with Other Tools
- Wells Score: Use PERC after low Wells probability
- D-dimer Testing: PERC positive patients may need D-dimer
- Clinical Gestalt: Always consider clinical suspicion
- Imaging: CT pulmonary angiogram for high suspicion
Important Considerations
Limitations
- Low specificity: Many patients will be PERC positive
- Clinical suspicion dependency: Only use in low suspicion
- Population specificity: Validated in specific populations
- Operator variability: Subjective interpretation of criteria
- Not diagnostic: Cannot rule in PE, only rule out
Special Populations
- Pregnant women: Estrogen criterion may not apply
- Elderly patients: Age criterion may be less discriminatory
- Chronic conditions: Baseline tachycardia may affect interpretation
- Post-operative patients: Recent surgery criterion important
Clinical Pearls
- PERC rule should only be used in patients with low clinical suspicion
- High clinical suspicion requires immediate evaluation regardless of PERC score
- PERC negative patients have < 1% probability of PE
- Consider alternative diagnoses in PERC negative patients
- PERC positive patients need further evaluation with D-dimer or imaging
- Use in conjunction with clinical judgment, not in isolation
- Document PERC score in medical records for quality assurance
Treatment Guidelines
PERC Negative (0 criteria)
- Low clinical suspicion: PE can be safely excluded
- Management: Consider alternative diagnoses
- Follow-up: Reassess if symptoms persist or worsen
- Documentation: Document PERC score and clinical reasoning
PERC Positive (≥1 criteria)
- Further evaluation: D-dimer testing or imaging recommended
- Clinical suspicion: Assess pre-test probability
- Imaging choice: CT pulmonary angiogram vs. ventilation-perfusion scan
- Anticoagulation: Consider empiric anticoagulation if high suspicion
Quality Assurance
Monitoring
- Track PERC negative patients for missed diagnoses
- Monitor imaging utilization rates
- Assess clinical outcomes and complications
- Review cases of missed PE for learning opportunities
Documentation
- Document PERC score and individual criteria
- Record clinical suspicion level
- Note decision-making process
- Include follow-up recommendations
The PERC rule is a valuable tool for safely excluding pulmonary embolism in low-risk patients, reducing unnecessary testing and improving resource utilization while maintaining patient safety.
References
- Kline JA, et al. Prospective multicenter evaluation of the pulmonary embolism rule-out criteria. J Thromb Haemost. 2008;6(5):772-780.
- Kline JA, et al. Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism. J Thromb Haemost. 2004;2(8):1247-1255.
- Righini M, et al. Age-adjusted D-dimer cutoff levels to rule out pulmonary embolism: the ADJUST-PE study. JAMA. 2014;311(11):1117-1124.
- Penaloza A, et al. Comparison of the unstructured clinician gestalt, the wells score, and the revised Geneva score to estimate pretest probability for suspected pulmonary embolism. Ann Intern Med. 2013;158(11):799-807.
- Kearon C, et al. Antithrombotic therapy for VTE disease: CHEST guideline and expert panel report. Chest. 2016;149(2):315-352.
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