PERC Rule for Pulmonary Embolism

Age ≥50

Heart Rate ≥100

O₂ Sat on Room Air <95%

Unilateral Leg Swelling

Hemoptysis

Recent Surgery or Trauma (≤4 weeks)

Prior PE or DVT

Hormone Use (OCP, HRT, or estrogen)

Criteria Positive: 0

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

Why Use

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.

When to 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, SaO ₂ ≥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.

Formula

If any of the following is/are present, PE cannot be ruled out: Age ≥50. HR ≥100. O₂ sat 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).

Pearls / Pitfalls

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.

Management

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.

More Information

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