PERC Rule Calculator
Use the PERC Rule (Pulmonary Embolism Rule-out Criteria) to identify low-risk patients for whom PE can be safely excluded without further testing.
What is the PERC Rule?
The PERC (Pulmonary Embolism Rule-out Criteria) is a clinical decision tool used to identify low-risk patients for whom pulmonary embolism (PE) can be safely ruled out without further testing. If all 8 PERC criteria are absent in a low-risk patient (gestalt <15%), PE is effectively excluded with negative predictive value >99.5%. This avoids unnecessary D-dimer testing, imaging, and radiation exposure in appropriate patients.
When should I use the PERC Rule?
Use PERC only in patients with LOW clinical suspicion for PE (physician gestalt <15% pretest probability). Do NOT use in moderate or high-risk patients. PERC is designed for emergency department screening of low-risk patients with chest pain, dyspnea, or other non-specific symptoms. If used appropriately, a negative PERC (all criteria absent) safely excludes PE without further testing. Positive PERC requires additional workup with Wells Score or D-dimer.
What does a negative PERC result mean?
A negative PERC (all 8 criteria absent) in a LOW-risk patient means PE can be safely excluded without D-dimer or imaging. Studies show <2% chance of PE in PERC-negative, low-risk patients. You can avoid radiation exposure, contrast reactions, false-positive cascades, and healthcare costs. However, this only applies if clinical suspicion is truly low (<15%). If any doubt exists about risk level, proceed with standard workup.
What does a positive PERC result mean?
A positive PERC (any criterion present) means you cannot use PERC to rule out PE. Proceed to formal risk stratification using Wells Score for PE, Geneva Score, or order D-dimer testing. PERC-positive does NOT mean PE is present—it simply means further evaluation is needed. Do not use PERC results alone to diagnose PE. Always correlate with clinical judgment and follow institutional protocols for PE evaluation.
What are the limitations of the PERC Rule?
PERC only applies to LOW-risk patients (gestalt <15%). Major limitations include: subjective determination of "low risk," physician gestalt varies, not validated in hospitalized patients, age criterion excludes many patients >50, may miss rare cases of PE. Never use PERC in moderate/high-risk patients, pregnant women (different criteria), children (not validated), or when clinical suspicion is significant. When in doubt, proceed with standard PE workup. PERC aids decision-making but doesn't replace clinical judgment.