PERC Rule for Pulmonary Embolism

Learn about the PERC Rule for ruling out pulmonary embolism in low-risk patients. Explore its eight criteria, interpretation, clinical significance, indications, and limitations.

PERC Rule Calculator

PERC Rule for Pulmonary Embolism

Enter patient data to determine if PE can be ruled out without further testing. All criteria must be met for PERC-negative result.

Age (years) *

Must be < 50 years

Heart Rate (bpm) *

Must be < 100 bpm

Oxygen Saturation (%) *

Must be ≥ 95% on room air

Additional Criteria (All must be "No")

Hemoptysis (coughing up blood)

Must be absent

Current estrogen use

Must be absent

Prior DVT or PE

Must be absent

Unilateral leg swelling

Must be absent

Recent surgery or trauma (past 4 weeks)

Must be absent

Disclaimer: This calculator is for educational purposes only and should not replace clinical judgment. The PERC rule is only valid for patients with low pre-test probability of PE. Always consult with a healthcare professional for medical decisions.

Pulmonary Embolism Rule-Out Criteria (PERC)

The PERC rule is a clinical decision tool designed to help clinicians exclude pulmonary embolism (PE) in patients who are already considered to have a low pre-test probability of the condition. By applying the PERC rule, unnecessary diagnostic testing can be minimized.

Key Principle:

All 8 criteria must be met for a patient to be considered PERC-negative (PE can be ruled out without further testing).

The 8 PERC Criteria

Vital Signs

Age < 50 years

Patient must be younger than 50 years of age.

Heart rate < 100 bpm

Resting heart rate must be less than 100 beats per minute.

Oxygen saturation ≥ 95%

Oxygen saturation on room air must be 95% or higher.

Clinical Findings

No hemoptysis

Absence of coughing up blood or blood-stained sputum.

No estrogen use

Not currently using exogenous estrogen (OCPs, HRT, etc.).

No prior DVT or PE

No history of deep vein thrombosis or pulmonary embolism.

No unilateral leg swelling

Absence of unilateral leg swelling, pain, or tenderness.

No recent surgery or trauma

No surgery or trauma requiring hospitalization in past 4 weeks.

Clinical Decision Making

PERC-Negative

• All 8 criteria met
• Low pre-test probability confirmed
• PE can be ruled out
• No further testing needed
• Consider alternative diagnoses

PERC-Positive

• One or more criteria not met
• Further testing required
• D-dimer testing recommended
• Consider imaging if D-dimer positive
• Close clinical monitoring

Validation and Performance

Clinical Validation

• Sensitivity: 97.4% (excellent for ruling out PE)
• Specificity: 21.9% (moderate for ruling in PE)
• Validation: Multiple studies with >14,000 patients
• Safety: Very low false negative rate

Important Limitations

• Only for low pre-test probability: Must assess clinical probability first (< 15%)
• Not for high-risk patients: Active cancer, thrombophilia, strong family history
• Clinical judgment required: Should not replace clinical assessment
• All criteria must be met: Even one positive criterion requires further testing
• Consider patient factors: Age, comorbidities, and clinical context matter
• Regular updates: Follow current clinical guidelines and updates

The PERC Rule (Pulmonary Embolism Rule-out Criteria) is a clinical decision-making tool designed to identify patients with such a low risk of pulmonary embolism (PE) that further diagnostic testing, such as D-dimer assays or imaging studies, is unnecessary. Developed by Dr. Jeffrey Kline and colleagues, the rule is particularly useful in the emergency department where chest pain and shortness of breath are common complaints.

The PERC Rule minimizes unnecessary testing and radiation exposure while reducing healthcare costs. It is applied only when the clinician’s pre-test probability of PE is already judged to be low (<15%). If all PERC criteria are negative, the risk of PE is considered low enough to safely forgo further workup.

The Eight PERC Criteria

For the PERC Rule to apply, all eight criteria must be satisfied (i.e., “negative”). If any are positive, further testing should be considered.

Criterion	Requirement for PERC Negative
Age	< 50 years
Heart rate	< 100 beats per minute
Oxygen saturation (on room air)	≥ 95%
Hemoptysis	Absent
Estrogen use	Absent (no oral contraceptives or hormone therapy)
Prior DVT or PE	Absent
Recent surgery or trauma	No surgery/trauma requiring hospitalization within past 4 weeks
Unilateral leg swelling	Absent

Interpretation

The PERC Rule is interpreted as follows:

All eight criteria negative: PE can be reasonably ruled out without further testing in low-risk patients.
Any criterion positive: Further evaluation with D-dimer testing, imaging (CT pulmonary angiography, V/Q scan), or additional clinical assessment is indicated.

Importantly, the PERC Rule should only be applied in patients with a low pre-test probability of PE. If the clinical suspicion is moderate or high, diagnostic testing should not be avoided regardless of PERC status.

Clinical Significance

The PERC Rule has become an important tool in emergency medicine for several reasons:

Reduces unnecessary testing: Helps avoid unnecessary D-dimer assays and CT scans, which can expose patients to radiation and contrast risks.
Supports rapid triage: Facilitates quick decision-making in busy emergency departments.
Evidence-based safety: Multiple validation studies confirm its safety in low-risk populations, with a miss rate for PE under 2% when applied correctly.
Cost-effective: Saves healthcare resources by reducing diagnostic overuse.

Indications for Use

The PERC Rule is indicated in:

Patients presenting with chest pain or dyspnea where PE is a differential diagnosis.
Emergency department evaluations where the clinician estimates a low pre-test probability of PE (<15%).
Settings where minimizing unnecessary imaging and laboratory testing is a priority.

Limitations

While highly useful, the PERC Rule has limitations:

Pre-test probability requirement: Should not be applied in patients with moderate or high suspicion for PE.
Age and comorbidity restrictions: Less reliable in older patients and those with multiple comorbidities.
Subjectivity: Requires clinician judgment to determine pre-test probability, which may vary between providers.
Not a substitute for clinical judgment: PERC is a rule-out tool, not a diagnostic test.