PERC Rule for Pulmonary Embolism

Each criterion adds one point when present (same framing as standard PERC worksheets). Score 0 in a patient with low pre-test probability supports ruling out PE without D-dimer or imaging. Only apply PERC when you are already evaluating for PE and the patient is low risk (often ≤15% probability).

Eligibility

Eight PERC criteria (1 point each if present)

Disclaimer: This tool supports education and shared clinical reasoning. It does not replace bedside assessment, institutional protocols, or specialist judgment. Always interpret PERC together with the full clinical picture.

PERC Rule: criteria, score, and use

Overview

The Pulmonary Embolism Rule-out Criteria (PERC) help clinicians avoid unnecessary testing in patients who have a low pre-test probability of acute PE and meet eight bedside criteria. When every criterion is absent (score 0) in that low-risk context, PE can be ruled out without D-dimer or imaging. If any criterion is present, the patient is not PERC-negative and further evaluation is appropriate.

Scoring (1 point per criterion)

Each row counts +1 when the finding is present. The published rule uses binary presence or absence of these eight items in a patient already judged to be low risk for PE.

Criterion	Points if present
Age ≥50 years	+1
Heart rate ≥100 bpm	+1
O₂ saturation on room air <95%	+1
Unilateral leg swelling	+1
Hemoptysis	+1
Recent surgery or trauma (≤4 weeks) requiring general anesthesia	+1
Prior PE or DVT	+1
Hormone use (OCPs, HRT, or estrogenic hormones in males or females)	+1

PERC-negative

Low pre-test probability and PERC score 0. PE can be ruled out without D-dimer or advanced imaging in appropriate settings.

Not PERC-negative

At least one criterion present while still low risk: PERC does not rule out PE; consider D-dimer and follow-up testing per guidelines.

Performance (literature)

In derivation and validation cohorts, PERC achieved high sensitivity for excluding PE among patients assessed as low risk, at the cost of lower specificity. Performance varies by setting and prevalence; always integrate local evidence and gestalt.

Limitations

• PERC is not intended for patients who are not being evaluated for PE.
• Do not apply PERC when suspicion is moderate or high; use risk-appropriate testing.
• Low pre-test probability must be established before interpreting a negative PERC result.
• Consider alternative diagnoses (for example pericardial disease) in pleuritic presentations.

Reference: Kline JA, Richardson DM, Than MP, 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.

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.

CalcMD.

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 for Pulmonary Embolism

Eligibility

Eight PERC criteria (1 point each if present)

PERC Rule: criteria, score, and use

Overview

Scoring (1 point per criterion)

PERC-negative

Not PERC-negative

Performance (literature)

Limitations

The Eight PERC Criteria

Interpretation

Clinical Significance

Indications for Use

Limitations