Differentiating Low-Risk and No-Risk PE Patients: The PERC Score

Background: Pulmonary embolism (PE) remains one of the most challenging diagnoses in emergency medicine. The Pulmonary Embolism Rule-out Criteria (PERC) score, a decision aid to reliably distinguish low-risk from very low-risk PE patients, has been derived and validated. Clinical Question: Can a subset of patients with sufficiently low risk for PE be identified who require no diagnostic testing? Evidence Review: The PERC score derivation and validation trials were located using PubMed and Web of Science. A critical appraisal of this research is presented. Results: One single-center and another multi-center validation trial both confirmed that the eight-item PERC score identified a very low-risk subset of patients in whom PE was clinically contemplated with a negative likelihood ratio 0.17 (95% confidence interval 0.11-0.25) in the larger trial. If applied, the rule would have identified 20% of potential PE patients as very low risk. Conclusion: The PERC score provides clinicians with an easily remembered, validated clinical decision rule that allows physicians to forego diagnostic testing for pulmonary embolus in a very low-risk population.