PERC Calculator
Pulmonary Embolism Rule-Out Criteria for safe PE exclusion
PERC Criteria Assessment
⚠️ Important Prerequisites
- • Use PERC rule only when clinical probability of PE is low (<15%)
- • Wells score should be ≤4 (or ≤1 in simplified version)
- • Patient should not have contraindications listed in limitations section
Select all criteria that apply to the patient. If ALL criteria are negative (none selected), pulmonary embolism can be safely ruled out without further testing.
PERC Assessment Results
Interpretation: Pulmonary embolism can be ruled out in this patient, as the overall risk is below 2%.
Recommendation: No further testing for PE is required. D-dimer testing can be avoided.
Next Steps: Consider alternative diagnoses for the patient's symptoms.
✅ PE Ruled Out
With all PERC criteria negative, the risk of PE is <2%. No further PE-specific testing is needed. Focus on alternative diagnoses for the patient's symptoms.
Clinical Example
Case: 35-year-old Female with Chest Pain
Presentation: Acute onset chest pain and shortness of breath
Wells Score: 2 points (low probability)
PERC Assessment:
- • Age <50 years ❌
- • Heart rate 85 bpm ❌
- • O₂ saturation 98% ❌
- • No unilateral leg swelling ❌
- • No hemoptysis ❌
- • No prior VTE history ❌
- • No recent trauma/surgery ❌
- • On oral contraceptives ✅
Result: PERC Positive (1/8 criteria) - Further testing required
PERC Rule Summary
PERC Negative (0/8)
PE risk <2% - No further testing needed
PERC Positive (≥1/8)
Cannot rule out PE - Further testing required
⚠️ PERC Rule Limitations
Do NOT use PERC rule if patient has:
- • Active cancer
- • Known thrombophilia
- • Strong family history of VTE
- • Using β-blockers (may mask tachycardia)
- • Leg amputation
- • Massive obesity (BMI ≥30)
- • Chronic hypoxemia <95%
Clinical Integration
Step 1: Wells Score
Calculate Wells score for PE probability
Step 2: PERC Rule
If Wells ≤4, apply PERC criteria
Step 3: Decision
PERC negative = No testing needed
⚕️ Medical Disclaimer
This calculator is for educational purposes only and should not replace clinical judgment.
Always consider the full clinical picture, patient history, and institutional protocols.
The PERC rule should only be applied in appropriate clinical scenarios with low pre-test probability.
Understanding the PERC Rule
What is the PERC Rule?
The Pulmonary Embolism Rule-Out Criteria (PERC) is a clinical decision rule that helps identify very low-risk patients who do not require further testing for pulmonary embolism.
Clinical Application
- •Reduces unnecessary D-dimer testing and imaging
- •Safe and effective PE rule-out strategy
- •Validated in emergency department settings
- •Reduces healthcare costs and patient anxiety
Evidence Base
Original Study (2005)
"Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism"
Validation Study (2007)
"Prospective multicenter evaluation of the pulmonary embolism rule-out criteria"
Performance Characteristics
- • Sensitivity: 97-100% for PE exclusion
- • Negative predictive value: >98%
- • Reduces testing in ~20% of patients
Important Clinical Pearls
Pre-Test Probability:
- • Only use when PE probability is low (<15%)
- • Wells score ≤4 is a good screening tool
- • Clinical gestalt is equally important
Clinical Decision Making:
- • PERC negative = No further PE testing
- • PERC positive = Proceed to D-dimer or imaging
- • Always consider alternative diagnoses