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    PERC Rule for Pulmonary Embolism

    Rules out PE if no criteria are present and pre-test probability is ≤15%.
    When to Use
    Why Use

    The PERC rule can be applied to patients where the diagnosis of PE is being considered, but the patient is deemed low-risk. A patient deemed low-risk by physician’s gestalt who is also <50 years of age, with a pulse <100 bpm, SaO2 ≥95%, no hemoptysis, no estrogen use, no history of surgery/trauma within 4 weeks, no prior PE/DVT and no present signs of DVT can be safely ruled out and does not require further workup.

    The Pulmonary Embolism Rule-out Criteria is utilized by physicians to avoid further testing for Pulmonary Embolism in patients deemed low risk.

    • The PERC Rule is a “rule-out” tool - all variables must receive a “no” to be negative.
    • The test is unidirectional: while PERC negative typically allows the clinician to avoid further testing, failing the rule doesn't force the clinician to order tests.
    • As a rule-out criteria, PERC is not meant for risk-stratification.
    • The physicians utilizing this rule must have a gestalt that the patient’s risk of PE is low (study used <15%).
    • The study was designed with a 1.8% test threshold. This took into account the risk associated with PE workup and treatment (i.e. CT radiation, anaphylaxis from contrast, bleeding from anticoagulation). For patients with a pre-test probability below this threshold the risk associated with starting a workup is equivalent to the chance of missing the diagnosis.
    • Emergency physicians have a low threshold for testing for PE.
    • This test rules out patients who are considered low-risk for PE based on clinical criteria alone.
    • PERC negative patients do not require utilization of the d-dimer, which has a high sensitivity but low specificity.
    • Low risk patients who are PERC negative avoid the risks associated with unnecessary testing and treatment for PE.


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    Creator Insights


    • In the setting of a low-risk patient who is not PERC negative, the physician should consider a d-dimer for further evaluation.
    • If the d-dimer is negative, and clinical gestalt determines a pre-test probability is <15% then, the patient does not require further testing for PE.
    • If the d-dimer is positive, further testing such as a CT-angiography or V/Q scan should be pursued.

    Critical Actions

    • There is no need to apply the PERC rule to those patients who are not being evaluated for PE.
    • If the patient is considered low-risk, PERC may help avoid further testing.
    • If the patient is moderate or high risk then PERC can not be utilized. Consider d-dimer or imaging based on risk.
    • Consider pericardial disease in patients with pleuritic complaints as well.


    If any of the following is/are present, PE cannot be ruled out:

    • Age ≥50.
    • HR ≥100.
    • SaO2 on room air <95%.
    • Unilateral leg swelling.
    • Hemoptysis.
    • Recent trauma or surgery.
    • Prior PE or DVT.
    • Hormone use (oral contraceptives, hormone replacement or estrogenic hormones use in males or female patients).

    Facts & Figures

    If any criteria are positive, the PERC rule is not satisfied and cannot be used to rule out PE in this patient.

    Evidence Appraisal

    The original article from 2004 was a prospective study with a derivation section and a validation section.

    • 3148 patients from 10 sites were included in the derivation.
    • 21 potential variables were included for analysis, with the 8 final variables selected from these.
    • 1427 low-risk and 382 very low-risk patients from 2 sites were included in the validation section.
    • In low-risk patients there was a sensitivity of 96% and specificity of 27%.
    • In very low-risk patients there was a sensitivity of 100% and specificity of 15%.
    • The false negative rate at 90 days in low-risk patients was 1.4% which is below the 1.8% testing threshold.

    A second multicenter validation was done in 2008. This expanded upon the initial validation study and defined low pretest probability as <15%

    • 8138 patients from 13 sites were included in the study. Some of these sites were included in the initial paper.
    • Clinical gestalt for a pretest probability of <15%, 15-40% or >40% was collected from the providers.
    • 20% of the cohort was deemed low risk (<15%)
    • For patients who were PERC negative and pre-test probability was <15% the false negative rate at 45 days was 1.0% with a sensitivity of 97.4% and specificity of 21.9%.
    Dr. Jeffrey Kline

    From the Creator

    Dr. Kline's comments about the PERC Rule for MDCalc:

    I derived the PERC rule to give some objective backing to the situation where you have considered PE in the active differential diagnosis, but really do not think any diagnostic test is necessary. To capture that concept scientifically, I validated the PERC rule to exclude PE with a gestalt pretest probability of <15% for PE and all eight criteria of the PERC rule are negative.

    About the Creator

    Jeffrey Kline, MD, is a professor of emergency medicine and physiology and the vice chair of research at Indiana University. Among other research, he has conducted clinical studies using breath-based methods to diagnose and assess the severity of PE. He co-founded BreathQuant Medical Systems Inc to advance practical applications of 16 patents for medical devices. Dr. Kline has published over 50 manuscripts in the area of PE.

    To view Dr. Jeffrey Kline's publications, visit PubMed

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