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The pulmonary embolism rule-out criteria (PERC) is an 8-variable clinical decision rule that identifies patients at low risk for pulmonary embolism (PE) to prevent unnecessary diagnostic testing in the evaluation of suspected PE in the emergency department (ED). The objective of this study was to determine PERC's safety and diagnostic use in our institution's ED population.We performed a retrospective analysis on consecutive adult patients evaluated with computed tomographic angiography (CTA) for suspicion of PE at our ED during the dates January 1, 2011, to December 31, 2011. Patients negative for all 8 PERC criteria (ie, “PERC [−]”) were considered to be at low risk for PE. All data were analyzed using SPSS-20 (SPSS Inc, Chicago, IL) to calculate the variables of interest and their respective 95% confidence intervals (95% CIs).During the 12-month study period, 729 subjects were evaluated with CTA for suspicion of PE. Ten subjects were excluded because of nondiagnostic imaging studies. After exclusion, 719 subjects were available for analysis. Prevalence of PE was 4.5%. PERC (−) had a sensitivity of 96.9% (95% CI, 84.3%-99.4%), a negative predictive value of 98.8% (95% CI, 93.5%-99.8%), and a negative likelihood ratio of 0.26 (95% CI, 0.04-1.82) when used as an independent diagnostic test to exclude PE.Use of PERC could have safely avoided 11.5% of CTAs, reducing potential patient harm, health care costs, and unnecessary diagnostic testing. Consistent with prior studies, PERC can be safely used to identify low-risk patients for whom further testing can be deferred.