Respiratory & Critical CareEvidence-Based Golden Standard
PERC Rule — Pulmonary Embolism Rule-Out
Eight clinical criteria that, when ALL negative in a patient already assessed as low pre-test probability, rule out pulmonary embolism without any D-dimer or imaging.
PERC (all 8 must be NEGATIVE to rule out PE):
Age ≥50 · HR ≥100 · SpO₂ <95% on room air · unilateral leg swelling · hemoptysis · recent surgery/trauma (≤4 wk) · prior PE/DVT · exogenous estrogen use
All 8 negative AND low clinical suspicion → PE ruled out (sensitivity 97.4%, false-negative rate <2%). Any positive → PERC fails, proceed to D-dimer/imaging.
Published Clinical Benchmark Cases
Clinical Parameters & Inputs
Computed OutputPERC Negative — PE ruled out (if low pre-test probability)
Negative
Diagnostic Interpretation
All 8 PERC criteria are negative. In a patient already judged LOW-risk by clinical Gestalt/Wells, PE is effectively ruled out and no D-dimer or CT is needed (test threshold met, <2% false-negative rate).
Calculation Breakdown
PERC Criteria
none positive =PERC Negative
Action
All negative + low suspicion → no further test =PERC Negative — PE ruled out (if low pre-test probability)
Clinical Decision Pearls
- PERC is ONLY valid after the clinician has already judged the patient to be low pre-test probability — it is not a stand-alone rule for everyone.
- PERC-negative patients still need clear return precautions and follow-up.
Limitations & Confounders
- Do not apply in intermediate or high pre-test probability — the rule was validated only in the low-risk group.
- Not validated in pregnancy, inpatients, or the critically ill.
Evidence & Citations
- Kline JA, Mitchell AM, Kabrhel C, Richman PB, Courtney DM. Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism. J Thromb Haemost. 2004;2(8):1247-1255.