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Am Fam Physician. 2018;98(4):250

Clinical Question

Can the pulmonary embolism rule-out criteria (PERC) clinical decision rule reduce the need for computed tomographic (CT) pulmonary angiography in low-risk patients with suspected pulmonary embolism (PE)?

Bottom Line

Use of the PERC clinical decision rule significantly reduces the need for CT pulmonary angiography in adults with an initial low-risk clinical estimate of suspected PE. (Level of Evidence = 1b)


The PERC decision rule is an eight-item set of clinical criteria, including arterial oxygen saturation of 94% or less, pulse rate of at least 100 beats per minute, patient age at least 50 years, unilateral leg swelling, hemoptysis, recent trauma or surgery, prior PE or deep venous thrombosis, and exogenous estrogen use. These investigators identified all consenting adults who presented to an emergency department with new-onset presence or worsening of shortness of breath or chest pain and a low clinical probability of PE (estimated by the treating physician as less than 15% probability). The patients (N = 962) were cluster-randomized (concealed allocation assignment) based on emergency department location to a control group or to an intervention group with a diagnostic workup that included an initial calculation of the PERC score. Patients who scored zero had no additional workup for PE. Patients with a PERC score above zero had a standard diagnostic workup that included d-dimer testing, followed by CT pulmonary angiography if the d-dimer result was positive (based on age-adjusted thresholds). The control group received only the standard workup without a preceding PERC calculation. The intervention strategy continued for six months, followed by a two-month washout period, and then the two groups crossed over to the other diagnostic strategy protocol. Individuals who assessed outcomes remained masked to group assignments. Follow-up occurred for 97% of patients at three months.

Using both intention-to-treat and per-protocol analyses, there was no significant difference in the proportion of patients in the PERC group who were given an initial diagnosis of PE compared with patients in the control group (1.5% vs. 2.7%). Only one PE (0.1%) was diagnosed during follow-up in the PERC group; none were diagnosed in the control group. CT pulmonary angiography occurred in significantly fewer patients in the PERC group than in the control group (13% vs. 23%; difference = −10%; 95% confidence interval, −13% to −6%).

Study design: Decision rule (validation)

Funding source: Government

Setting: Emergency department

Reference:FreundYCachanadoMAubryAet alEffect of the pulmonary embolism rule-out criteria on subsequent thromboembolic events among low-risk emergency department patients: the PROPER randomized clinical trial. JAMA2018;319(6):559–566.

POEMs (patient-oriented evidence that matters) are provided by Essential Evidence Plus, a point-of-care clinical decision support system published by Wiley-Blackwell. For more information, see Copyright Wiley-Blackwell. Used with permission.

For definitions of levels of evidence used in POEMs, see

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This series is coordinated by Natasha J. Pyzocha, DO, contributing editor.

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