PERC Calculator - Pulmonary Embolism Rule-Out Criteria

The Pulmonary Embolism Rule-Out Criteria relies on a binary scoring logic. To achieve a negative PERC result (meaning PE is safely ruled out without further testing), the patient must present with a low clinical pre-test probability of PE (< 15%) and must score negative across all eight clinical criteria: age under 50, heart rate under 100 beats per minute, oxygen saturation on room air at 95% or greater, no unilateral leg swelling, no hemoptysis, no recent surgery or trauma within four weeks, no prior history of deep vein thrombosis or pulmonary embolism, and no use of oral contraceptives or hormone therapy. If even a single criterion is positive, the PERC rule is failed, and further diagnostic evaluation such as a D-dimer test or CT angiogram may be indicated.

Consider a 34-year-old female presenting to the emergency department with mild, acute shortness of breath. Her clinical evaluation reveals the following metrics: Age is 34 (passes), heart rate is 88 bpm (passes), room air oxygen saturation is 98% (passes), there is no unilateral leg swelling (passes), she reports no hemoptysis (passes), no recent trauma or surgery (passes), no prior DVT/PE history (passes), but she currently takes oral contraceptive pills (fails). Because she triggers one positive criterion (contraceptive use), her overall PERC result is positive. Consequently, the clinician cannot rule out pulmonary embolism using the PERC rule alone and must proceed with further risk stratification, such as ordering a D-dimer blood test.

Always establish that the patient has a low pre-test probability of pulmonary embolism before applying the PERC rule; it should never be used in moderate- or high-risk populations. Ensure accurate measurement of vital signs, particularly room air oxygen saturation, as supplemental oxygen can mask underlying hypoxemia and lead to a false-negative assessment. Remember that a positive PERC score does not confirm a pulmonary embolism; it simply indicates that further diagnostic testing is required to rule it in or out definitively.