PERC Rule Calculator — Pulmonary Embolism Rule-Out Criteria (Low-Risk Patients)
Apply the 8-item PERC rule in low-risk emergency department patients with suspected PE to safely exclude pulmonary embolism without D-dimer testing or imaging.
PERC Rule Calculator
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This calculator is for informational and educational purposes. Results should be interpreted with clinical judgment and local guidelines.
What is the PERC Rule (Pulmonary Embolism Rule-Out Criteria)?
The PERC rule (Pulmonary Embolism Rule-Out Criteria) is a 8-item clinical decision rule developed by Dr. Jeffrey Kline and colleagues in 2004 to safely exclude pulmonary embolism (PE) in patients deemed to be at low pre-test probability (e.g. Wells score < 2 or gestalt < 15%) WITHOUT ordering a D-dimer blood test or CT pulmonary angiography (CTPA). If a low-risk patient meets ALL 8 criteria (PERC negative, score 0), the post-test probability of PE is less than 1.8%—below the threshold where diagnostic testing risks (radiation, contrast nephropathy, false positive anticoagulation) exceed the risk of missed PE.
PERC Negative = All 8 criteria satisfied (Age < 50, HR < 100, SpO₂ ≥ 95%, No unilateral leg swelling, No hemoptysis, No recent surgery/trauma, No prior DVT/PE, No estrogen use). Post-test PE risk < 1.8% → No D-dimer or CTPA needed.
When to Use the PERC Rule Calculator
- Emergency department evaluation of chest pain or dyspnea in patients stratified as LOW pre-test probability for PE (Wells score ≤ 1.5 or low clinical gestalt).
- Avoiding unnecessary D-dimer testing in young, healthy low-risk emergency patients, reducing false positives and unnecessary CTPA scans.
The 8 PERC Rule Criteria Breakdown
PERC Criteria Evaluation
PERC Negative = 0 criteria present. Any 1 criterion present = PERC positive.
Age 35, HR 88, SpO₂ 98%, no leg swelling, no hemoptysis, no surgery, no prior VTE, no estrogen → PERC Negative (PE ruled out without D-dimer).
Variables
1. Age < 50 years (boolean)
Patient must be under 50 years old.
2. Pulse / HR < 100 bpm (boolean)
Heart rate strictly under 100 beats per minute.
3. Pulse Oximetry SpO₂ ≥ 95% (boolean)
Oxygen saturation ≥ 95% on room air.
4. No Unilateral Leg Swelling (boolean)
No clinical signs of unilateral deep vein thrombosis.
5. No Hemoptysis (boolean)
No history of coughing up blood.
6. No Recent Surgery or Trauma (boolean)
No surgery or trauma requiring endotracheal anesthesia or hospitalization within 4 weeks.
7. No Prior DVT or PE (boolean)
No documented history of venous thromboembolism.
8. No Estrogen Use (boolean)
No oral contraceptives, hormone replacement therapy, or estrogenic medication.
MUST only be applied AFTER determining the patient is LOW RISK (Wells ≤ 1.5). Do not apply PERC to moderate or high-risk patients!
PERC Rule Clinical Decision Pathways
Guidelines per ACEP (American College of Emergency Physicians) and PROPER trial.
| Range | Classification | Health Risk |
|---|---|---|
| PERC Negative (0 criteria met) | PE Ruled Out (No Testing) | Post-test PE probability < 1.8%. Stop workup! No D-dimer, no CTPA. |
| PERC Positive (≥ 1 criterion met) | Proceed to D-Dimer Test | Cannot rule out PE by PERC alone. Order D-dimer assay. |
The PROPER randomized controlled trial (JAMA 2018) confirmed that PERC rule implementation safely reduced CTPA imaging by 10% without increasing missed PE events.
Limitations & Clinical Warnings
Do NOT use PERC in moderate or high-risk PE patients (Wells > 1.5).
PERC is not validated for patients evaluated in the outpatient clinic setting without acute ED presentation.
If room air SpO₂ is < 95% or HR ≥ 100 bpm, PERC is positive and D-dimer is required.
Medical Disclaimer
PERC rule requires strict adherence to all 8 items. Missing even one item invalidates the rule-out.
References & Citations
- Kline JA, Mitchell AM, Kabrhel C, et al.. “Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism”. Journal of Thrombosis and Haemostasis. 2004. 2(8): 1247–1255. PMID: 15304025 | DOI: 10.1111/j.1538-7836.2004.00790.x
- Freund Y, Cachanado M, Aubry A, et al.. “Effect of the Pulmonary Embolism Rule-Out Criteria on Imaging Rate in Patients With Low Clinical Risk (PROPER Trial)”. JAMA. 2018. 319(6): 559–566. PMID: 29435586
Medically Reviewed
Reviewed by CliniqWise Clinical Advisory Board — Emergency Medicine Panel · Last updated: 2026-08-27 · Next review: 2027-02-27
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