The Pulmonary Embolism Rule-out Criteria (PERC Rule) is a validated clinical decision tool designed to help clinicians exclude pulmonary embolism (PE) in patients with a low pretest probability. Developed in the early 2000s, it reduces unnecessary testing such as D-dimer assays and imaging, which can be costly and expose patients to risks.

The rule is based on eight yes/no criteria: age less than 50 years, pulse under 100 beats per minute, oxygen saturation of at least 95% on room air, no hemoptysis, no estrogen use, no prior venous thromboembolism, no recent surgery or trauma requiring hospitalization, and no unilateral leg swelling. If all eight criteria are met (all negative), and the clinician’s overall gestalt suggests a low probability of PE, the likelihood of pulmonary embolism is very low.

This tool is particularly useful in emergency and acute care settings, where rapid decisions are essential. Its primary strength lies in its ability to reduce unnecessary investigations in low-risk patients, improving efficiency while maintaining safety. However, it should not be used in patients with moderate or high suspicion for PE, as false reassurance could delay lifesaving treatment.