PERC Rule for Pulmonary Embolism

What is the PERC Rule?

The Pulmonary Embolism Rule-out Criteria (PERC) is a clinical decision rule developed to identify patients with a low risk of pulmonary embolism (PE) in whom further diagnostic testing can be safely avoided. It was developed by Dr. Jeffrey Kline and colleagues and published in 2004.

The PERC rule consists of eight objective criteria that can be assessed at the bedside or in the emergency department. If all criteria are negative (i.e., PERC negative), the risk of PE is considered very low (less than 2%), and further testing may not be necessary in patients with a low clinical suspicion for PE.

The Eight PERC Criteria

A patient is considered PERC positive if ANY of the following criteria are present:

• Age ≥ 50 years
• Heart rate ≥ 100 beats per minute
• Oxygen saturation on room air < 95%
• Unilateral leg swelling
• Hemoptysis
• Recent trauma or surgery (within 4 weeks)
• Prior history of venous thromboembolism (DVT or PE)
• Hormone use (estrogen-containing oral contraceptives or hormone replacement therapy)

If ALL criteria are negative (PERC negative), the patient is considered at very low risk for PE.

Clinical Application

The PERC rule should only be applied to patients who:

• Have a low clinical suspicion for PE
• Are being considered for diagnostic testing for PE

The PERC rule is intended to be used as a "rule-out" tool, not as a diagnostic test for PE. It helps clinicians identify patients in whom the risk of PE is so low that the risks of diagnostic testing (radiation exposure, contrast reactions, etc.) outweigh the benefits.

Interpretation

Validation and Performance

The PERC rule has been validated in multiple studies and settings:

• Sensitivity: 96-100% (high sensitivity is crucial for a rule-out tool)
• Specificity: 20-25% (relatively low, as the rule is designed to be sensitive)
• Negative predictive value: 99-100% in low-risk populations

A meta-analysis published in 2016 found that the PERC rule has a failure rate of approximately 0.9% when applied to patients with a low clinical probability of PE, confirming its safety as a rule-out tool.

Limitations

The PERC rule has several important limitations:

• Only applicable to patients with a low clinical suspicion for PE
• Not validated in inpatients or patients with high-risk comorbidities
• Should not be used in isolation; clinical judgment remains essential
• Performance may vary in different populations and settings
• Not designed to diagnose PE, only to rule it out in low-risk patients

Diagnostic Pathway for Suspected PE

A typical diagnostic approach for suspected PE might include:

1. Clinical assessment and risk stratification (e.g., using Wells score or Geneva score)
2. For low-risk patients, apply the PERC rule
3. If PERC negative, consider no further testing
4. If PERC positive or moderate/high clinical risk, proceed with D-dimer testing
5. If D-dimer positive or high clinical risk, proceed with imaging (CT pulmonary angiography or V/Q scan)

References

1. Kline JA, Mitchell AM, Kabrhel C, Richman PB, Courtney DM. Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism. J Thromb Haemost. 2004;2(8):1247-1255.
2. Singh B, Mommer SK, Erwin PJ, Mascarenhas SS, Parsaik AK. Pulmonary embolism rule-out criteria (PERC) in pulmonary embolism--revisited: a systematic review and meta-analysis. Emerg Med J. 2013;30(9):701-706.
3. Freund Y, Cachanado M, Aubry A, et al. Effect of the Pulmonary Embolism Rule-Out Criteria on Subsequent Thromboembolic Events Among Low-Risk Emergency Department Patients: The PROPER Randomized Clinical Trial. JAMA. 2018;319(6):559-566.
4. Raja AS, Greenberg JO, Qaseem A, et al. Evaluation of Patients With Suspected Acute Pulmonary Embolism: Best Practice Advice From the Clinical Guidelines Committee of the American College of Physicians. Ann Intern Med. 2015;163(9):701-711.