PERC Rule Calculator — Pulmonary Embolism Rule-Out Criteria
Apply the PERC Rule to rule out pulmonary embolism without D-dimer or imaging in low-risk ED patients. 8-criteria clinical decision tool with a false-negative rate of only 1.0%.
PERC Criteria Assessment
All 8 criteria must be absent (No) to rule out PE
Prerequisite: Low Pre-Test Probability
PERC must ONLY be applied when clinical pre-test probability is < 15% (low gestalt or Wells PE Score ≤ 4). Do NOT apply to moderate or high-risk patients.
Is the patient 50 years of age or older?
Any tachycardia at ANY point during ED evaluation, not just at time of assessment. Beta-blockers may mask tachycardia.
Must be on room air. SpO2 > 94% (effectively ≥ 95%) is required to meet this criterion.
Any coughing up of blood
Oral contraceptives, hormone replacement therapy, or any exogenous estrogenic hormones
Any history of venous thromboembolism (PE or DVT)
Clinical signs of DVT — unilateral swelling in one leg
Surgery or trauma within 4 weeks requiring general anesthesia or hospitalization
Mnemonic: HAD CLOTS
PERC Result
Answer all 8 criteria to see result
About This Calculator
The Pulmonary Embolism Rule-out Criteria (PERC) is a clinical decision rule that identifies emergency department patients with suspected PE who are at sufficiently low risk that no further diagnostic testing (D-dimer, CT pulmonary angiography) is needed.
When to Use PERC
PERC should ONLY be applied when the clinician's pre-test probability assessment is LOW (< 15%). This is the single most important prerequisite. Applying PERC to moderate- or high-risk patients is dangerous and is the most common misuse of the rule.
How PERC Works
All 8 criteria must be negative (absent) for PERC to rule out PE. If ANY single criterion is positive, PERC cannot exclude PE, and further workup is indicated.
The 1.8% Testing Threshold
The PERC creators established that below 1.8% post-test probability, the harms of testing (CTPA radiation, contrast nephropathy, false positives leading to unnecessary anticoagulation) exceed the risk of a missed PE. PERC is designed to bring post-test probability below this threshold.
Validation
PERC was derived from 3,148 patients (2004), validated in 8,138 patients across 13 US EDs (2008), and confirmed in the PROPER randomized trial (1,916 patients, JAMA 2018). The false-negative rate in low-risk patients is approximately 1.0% at 45 days.
Formula
PERC Rule = All 8 criteria must be ABSENT to rule out PE (binary: negative or positive)The PERC Rule uses 8 binary criteria. ALL must be absent (negative) to rule out pulmonary embolism: • Age < 50 years • Heart rate < 100 bpm (at any point during evaluation) • SpO2 > 94% on room air • No hemoptysis • No exogenous estrogen use • No prior PE or DVT • No unilateral leg swelling • No recent surgery or trauma (within 4 weeks) If ANY single criterion is positive, PERC cannot rule out PE. Mnemonic: "HAD CLOTS" — Hormone use, Age ≥ 50, DVT/PE history, Coughing blood, Leg swelling, O2 sat < 95%, Tachycardia, Surgery/trauma.
Clinical Considerations
- •PERC must ONLY be applied when pre-test probability is LOW (< 15%). Applying to moderate/high-risk patients is dangerous.
- •PERC is a rule-OUT tool, NOT a screening tool. Do not apply to all chest pain patients.
- •A PERC-positive result does NOT mean the patient has PE. Positive LR is only 1.23.
- •NOT validated for pregnant or postpartum patients. Use YEARS algorithm or D-dimer pathway instead.
- •Check vital signs from the ENTIRE visit — any tachycardia or hypoxemia at any point counts.
- •Pleuritic chest pain (OR 1.53 for PE) is NOT a PERC criterion. Factor it into your clinical gestalt.
- •Documentation is critical. A $10M malpractice verdict hinged on inadequate PERC documentation.
Limitations
- •Binary age cutoff at 50 — a 51-year-old with no other risk factors automatically fails
- •All women on oral contraceptives fail PERC despite low absolute VTE risk
- •Not validated for pregnant or postpartum patients
- •European settings with higher PE prevalence (21-30%) show higher failure rates
- •No graduated response — 1 failed criterion treated the same as 6 failed criteria
- •Does not include pleuritic chest pain (OR 1.53 for PE, higher than hemoptysis)
- •Vital sign "snapshot" problem — clinicians may miss earlier abnormal readings
- •Not designed for referred/secondary care populations (failure rate rises to 6%)
Interpretation Guide
| Range | Classification | Recommendation |
|---|---|---|
| <-0 | PERC Negative — PE Ruled Out | PE can be clinically ruled out. No D-dimer or imaging is needed. Safe to discharge with appropriate follow-up instructions. Document PERC result and each criterion assessed. |
| <-9 | PERC Positive — Cannot Rule Out PE | PE cannot be ruled out by clinical criteria alone. Consider D-dimer (age-adjusted if > 50) or proceed to Wells Score. A positive PERC does NOT confirm PE — it simply means clinical exclusion is not sufficient (positive LR = 1.23). |
Frequently Asked Questions
What is the PERC Rule?
The PERC Rule (Pulmonary Embolism Rule-out Criteria) is a clinical decision tool that uses 8 binary criteria to rule out pulmonary embolism without D-dimer or imaging in low-risk emergency department patients. All 8 criteria must be absent for PE to be ruled out. It was developed by Dr. Jeffrey Kline and validated in over 8,000 patients.
What are the 8 PERC criteria?
The 8 PERC criteria (mnemonic: HAD CLOTS) are: (1) Age < 50, (2) Heart rate < 100, (3) SpO2 > 94% on room air, (4) No hemoptysis, (5) No exogenous estrogen use, (6) No prior PE/DVT, (7) No unilateral leg swelling, (8) No surgery/trauma within 4 weeks. All 8 must be absent to rule out PE.
What does PERC negative mean?
PERC negative means all 8 criteria are absent and PE can be clinically ruled out. No D-dimer or CT pulmonary angiography is needed. The false-negative rate is approximately 1.0% at 45 days, which is below the 1.8% testing threshold where the harms of testing exceed the risk of a missed PE.
When should you use the PERC Rule?
PERC should ONLY be used when the clinician's pre-test probability for PE is LOW (< 15%), as assessed by clinical gestalt or a low Wells Score. This is the critical prerequisite. Never apply PERC to moderate- or high-risk patients. PERC is a rule-out tool for patients where PE is considered but seems unlikely.
What is the sensitivity of the PERC Rule?
PERC has a sensitivity of 97.4% and specificity of 21.9% in the multicenter validation study (Kline 2008). The false-negative rate is 1.0% at 45 days in low-risk patients. The PROPER trial (JAMA 2018) confirmed non-inferiority with only 0.1% thromboembolic events in the PERC group.
What is the difference between PERC and Wells for PE?
Wells Score for PE estimates pre-test probability of PE and determines which patients need D-dimer or imaging. PERC rules OUT PE entirely in patients already assessed as low-risk. In the PE diagnostic algorithm: (1) Wells determines pre-test probability, (2) if low-risk, apply PERC, (3) if PERC negative, stop — no further testing needed.
Can you use PERC in pregnancy?
No. PERC is NOT validated for pregnant or postpartum patients. Among PERC-negative PE cases, pregnancy occurred in 4% vs 1% of PERC-positive cases. Use the YEARS algorithm or D-dimer pathway instead for pregnant patients with suspected PE.
What is the false negative rate of the PERC Rule?
In the multicenter validation (Kline 2008), the false-negative rate was 1.0% at 45 days when applied to patients with pre-test probability < 15%. In pooled data, the missed PE rate was 0.32% (44 of 13,855 cases). This is below the 1.8% testing threshold established by PERC creators.
What PERC criteria are most commonly failed?
Age ≥ 50 is the most commonly failed criterion, as it automatically disqualifies a large portion of ED patients. Exogenous estrogen use is the second most discussed, as all women on oral contraceptives fail PERC despite a low absolute VTE risk increase. Heart rate ≥ 100 from other causes (pain, anxiety) is also common.
If PERC is positive, does the patient have PE?
No. A positive PERC result (one or more criteria present) does NOT mean the patient has PE. The positive likelihood ratio is only 1.23, which barely moves the post-test probability. It simply means PE cannot be clinically excluded and further workup (D-dimer, Wells Score, or imaging) is indicated.
References
1. 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. doi: 10.1111/j.1538-7836.2004.00790.x
View Source →2. Kline JA, Courtney DM, Kabrhel C, et al.. Prospective multicenter evaluation of the pulmonary embolism rule-out criteria. Journal of Thrombosis and Haemostasis. 2008. doi: 10.1111/j.1538-7836.2008.02944.x
View Source →3. Freund Y, Cachanado M, Aubry A, et al.. Effect of the Pulmonary Embolism Rule-Out Criteria on Subsequent Thromboembolic Events Among Low-Risk ED Patients: The PROPER Randomized Clinical Trial. JAMA. 2018. doi: 10.1001/jama.2017.21904
View Source →4. Konstantinides SV, Meyer G, Becattini C, et al.. 2019 ESC Guidelines for the diagnosis and management of acute pulmonary embolism. European Heart Journal. 2020. doi: 10.1093/eurheartj/ehz405
View Source →5. Lim W, Le Gal G, Bates SM, et al.. American Society of Hematology 2018 guidelines for management of venous thromboembolism: diagnosis of venous thromboembolism. Blood Advances. 2018. doi: 10.1182/bloodadvances.2018024828
View Source →Last updated: 2026-02-24
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