Criteria to rule out pulmonary embolism without further testing

What it is and when to use it

The PERC Rule (Pulmonary Embolism Rule-out Criteria) is a set of 8 clinical criteria that, in patients with a low pre-test probability of pulmonary embolism (PE), allows PE to be ruled out without ordering a D-dimer or imaging. The 8 criteria are: age <50 years, heart rate <100/min, SaO₂ ≥95% on room air, no hemoptysis, no estrogen use, no surgery or trauma requiring hospitalization in the prior 4 weeks, no prior DVT or PE, and no unilateral leg swelling. It was derived by Kline et al. (2004) and is endorsed by the American College of Physicians (ACP) and incorporated by the European Society of Cardiology (ESC) as an option in patients with low clinical suspicion.

How to interpret it

The rule applies only after clinical judgment has already established a LOW pre-test probability of PE (for example, low-risk clinical gestalt or a Wells score ≤4, i.e. "PE unlikely"). If all 8 criteria are met (PERC negative), the probability of PE is low enough (<2%) to rule it out without further testing. If any of the 8 criteria is not met (PERC positive), PE cannot be excluded and workup proceeds with D-dimer and, depending on the result, imaging (CT pulmonary angiography or V/Q scan). PERC is not scored additively: a single criterion being present makes it positive.

Limitations and when not to use it

PERC is validated only in low-risk outpatient emergency department patients; it should not be applied in populations with high PE prevalence or in hospitalized patients. It is not valid as a universal screening tool: applying it to patients with intermediate or high pre-test probability can miss PE. Use caution in populations with baseline tachycardia, pregnant patients (estrogen criterion and altered physiology), or patients with risk factors not captured by the criteria. PERC does not diagnose PE or assess its severity; it is solely a rule-out tool in low-risk patients.

Frequently asked questions

When can I use the PERC rule?

Only after you have judged the patient to have a low clinical probability of PE (low-risk gestalt or a Wells score ≤4, i.e. "PE unlikely") in an emergency department setting. If probability is high, PERC does not apply.

If PERC is negative, do I still need a D-dimer?

No. If all 8 criteria are met in a low-risk patient, the probability of PE is low enough to rule it out without a D-dimer or imaging, avoiding unnecessary testing.

How many criteria can fail for PERC to be positive?

None. The rule is negative only when all 8 criteria are met simultaneously; the presence of even one criterion makes it positive and requires further workup.