Rules out PE in low-risk patients
Total Score
Criteria satisfied (Score 0). PE ruled out. No D-dimer needed.
Disclaimer: The clinical scoring and algorithms on this platform are intended strictly for professional informational purposes. They do not constitute a definitive medical diagnosis, treatment, or clinical decision. The final judgment and responsibility lie with the treating physician.
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The PERC (Pulmonary Embolism Rule-out Criteria) rule is an 8-item clinical tool developed to completely rule out PE in patients with a low pre-test probability (<15%). If all criteria are negative, the chance of PE falls below 2%, allowing safe discharge without the need for D-Dimer testing.
The PERC rule MUST only be applied to low-risk patients (Wells score <2 or low clinical gestalt). It is not designed to risk-stratify moderate or high-risk patients; those patients require D-Dimer or CTPA.
Kline JA, Mitchell AM, Kabrhel C, et al. Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism. J Thromb Haemost. 2004;2(8):1247-1255.
Disclaimer: The clinical scoring and algorithms on this platform are intended strictly for professional informational purposes. They do not constitute a definitive medical diagnosis, treatment, or clinical decision. The final judgment and responsibility lie with the treating physician.
The PERC Rule is only valid as a rule-OUT tool in patients where the clinician has already estimated a LOW pre-test probability for PE (typically < 15% by gestalt). If pre-test probability is not low, proceed directly to D-dimer or CT pulmonary angiography. All 8 criteria must be absent (score = 0) to declare PERC-negative. A single positive criterion mandates further workup with D-dimer (age-adjusted if > 50) or imaging. The PERC Rule is not a scoring system — it is a binary pass/fail clinical decision rule.
The strongest validation of the PERC Rule comes from the PROPER randomised controlled trial (Freund et al., JAMA 2018), which showed that a gestalt low pre-test probability + PERC-negative approach was non-inferior to D-dimer testing, with a 3-month PE rate of 0% in the PERC-negative arm. The key is 'gestalt' — the attending physician must independently believe the pre-test probability is low BEFORE applying PERC. Applying PERC to intermediate-risk patients is incorrect use and can result in missed PE.
Exogenous estrogen (oral contraceptives, hormone replacement, tamoxifen) is a positive PERC criterion if currently in use — even in a young woman who appears otherwise low-risk. The O2 saturation threshold is < 95% on room air; pulse oximetry must be obtained in ambient air, not on supplemental oxygen. The "prior DVT/PE" criterion refers to any prior personal history, regardless of how long ago. Do not confuse PERC with the Wells PE Score — Wells is used to select the appropriate next diagnostic step (D-dimer vs CT-PA), while PERC is used to avoid any testing at all.