How this calculator works
PERC is an all-negative checklist intended for patients already judged to have a low pretest probability of PE. The eight negative requirements are age below 50, pulse below 100, room-air saturation at least 95%, no unilateral swelling, no haemoptysis, no prior VTE, no recent qualifying surgery/trauma and no exogenous oestrogen. This page counts positive findings for transparency; a nonzero count is not a probability score. It cannot be applied to unselected patients or used as home triage. The result is an estimate for information only and is not medical advice.
Formula
PERC negative requires all eight findings absent, plus an appropriate clinician-assessed low pretest probability. Any positive finding means the rule cannot exclude PE.
Worked example
A low-risk 40-year-old with pulse 80, room-air saturation 98% and all remaining criteria absent has count 0. Age exactly 50 makes the count 1.
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Frequently asked questions
Can I use PERC without a pretest assessment?
No. Low pretest probability must be established before considering the rule.
Does saturation exactly 95% pass?
Yes. The negative criterion is at least 95% on room air.
Does a positive PERC diagnose PE?
No. It means this rule cannot exclude PE and further assessment depends on the clinical pathway.