PERC Rule Calculator — Pulmonary Embolism Rule-Out Criteria
The PERC (Pulmonary Embolism Rule-out Criteria) rule allows clinicians to exclude PE in patients with LOW pre-test probability without ordering a D-dimer. Score any one criterion as "Yes" and further testing is needed.
Age ≥ 50
Heart rate ≥ 100 bpm
O₂ saturation < 95% on room air
Unilateral leg swelling
Hemoptysis (coughing blood)
Recent surgery or trauma (≤ 4 weeks)
Prior DVT or PE
Exogenous estrogen use
Score 0 = PERC Negative (PE ruled out in low pre-test probability patients); any score ≥ 1 = PERC Positive
How does this calculator work?
The PERC rule checks 8 binary criteria (age ≥ 50, HR ≥ 100, SpO₂ < 95%, leg swelling, hemoptysis, recent surgery, prior DVT/PE, estrogen use). Score 0 = PERC Negative — PE can be excluded without D-dimer in LOW pre-test probability patients (miss rate < 2%). Any positive criterion requires D-dimer testing.
Formula
How this is calculated
The PERC rule, derived by Kline et al. (2004) and validated in the PERC-IV study, applies exclusively to patients already judged to have a LOW pre-test probability of pulmonary embolism — typically a Wells score < 2. In that population, a negative PERC rule (all 8 criteria absent) carries a miss rate below 2%, the traditional threshold used to exclude PE without imaging.
The eight criteria are each independently associated with an elevated likelihood of PE: age ≥ 50, heart rate ≥ 100 bpm, oxygen saturation < 95% on room air, unilateral leg swelling, hemoptysis, recent surgery or trauma within four weeks, prior documented DVT or PE, and current exogenous estrogen use. A single "Yes" makes the PERC rule positive — the patient must proceed to D-dimer and potentially CT pulmonary angiography.
Critical caveat: this tool is a clinical decision support aid, not a stand-alone diagnostic. Pre-test probability assessment (Wells criteria, physician gestalt) must happen first. A PERC-negative result in a patient with moderate or high pre-test probability is inappropriate and unsafe. Never apply PERC to any patient who warrants imaging on clinical grounds alone.
Frequently asked questions
Only in patients with LOW pre-test probability (e.g. Wells score < 2). A PERC-negative result in that specific population has a miss rate below 2% and is considered sufficient to exclude PE without further testing. In moderate- or high-probability patients, PERC is not applicable — D-dimer and/or CT are required regardless.
Order a high-sensitivity D-dimer. If the D-dimer is elevated (above the age-adjusted cutoff for patients over 50), proceed to CT pulmonary angiography (CTPA). A normal D-dimer in a low-probability patient effectively excludes PE without imaging, even if PERC is positive.
No. Pregnancy, active malignancy, and other conditions substantially raise baseline PE risk and pre-test probability. These patients generally fall outside the "low pre-test probability" category in which PERC was validated. They require D-dimer testing (with pregnancy-specific cutoffs if pregnant) and clinical judgment guided by specialist input.
Also known as
TG we-Calculate Editorial Team. (2026). PERC Rule Calculator — Pulmonary Embolism Rule-Out Criteria [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/perc-calculator
TG we-Calculate Editorial Team. "PERC Rule Calculator — Pulmonary Embolism Rule-Out Criteria." TG we-Calculate. 2026. https://we-calculate.com/calculator/perc-calculator.
TG we-Calculate Editorial Team, "PERC Rule Calculator — Pulmonary Embolism Rule-Out Criteria," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/perc-calculator
@misc{wecalculate_perc_calculator, title = {PERC Rule Calculator — Pulmonary Embolism Rule-Out Criteria}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/perc-calculator}}, year = {2026}, note = {TG we-Calculate} }
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