PERC Rule Calculator
What is PERC Rule Calculator
PERC (Pulmonary Embolism Rule-out Criteria) is a set of eight yes/no items: age 50 or older, heart rate 100 or higher, oxygen saturation below 95%, unilateral leg swelling, hemoptysis, recent surgery or trauma, prior DVT or PE, and estrogen use. In a patient already judged to be low pretest probability, all eight being negative rules out PE without a D-dimer or imaging. A single positive item means PERC cannot exclude PE.
How to use
- Confirm you have already judged the patient to be low pretest probability.
- Tick every criterion that is present.
- Read whether PERC is negative or positive from the result.
- If negative, PE is ruled out; if positive, continue with D-dimer or imaging.
When to use it
Got a low-risk patient with chest pain or dyspnea and want to avoid an unnecessary D-dimer? Run the eight criteria: if all are negative, PERC rules out PE and spares the workup, while a single positive (say age 52 or a heart rate of 104) means you keep going. Best used at triage or on the first assessment, only after you have decided the pretest probability is genuinely low.
Frequently asked questions
When can I apply the PERC rule?
Only when you have already judged the pretest probability of PE to be low on clinical grounds. PERC is not a screening test for every patient with chest pain, and it should not override a moderate or high clinical suspicion.
What does a negative PERC mean?
All eight criteria are negative. In a low-risk patient this rules out PE without a D-dimer, because the residual risk falls below the testing threshold. If any single criterion is positive, PERC is positive and PE is not excluded.
Does PERC replace the Wells score?
No. Wells estimates pretest probability; PERC is applied after you decide the probability is low, to see if you can skip the D-dimer entirely. They are used in sequence, not interchangeably.
Can I share this calculator with the criteria pre-filled?
Yes. The URL updates as you tick each item. Copy it from the address bar or use the Copy link button, and anyone who opens it sees the same PERC result ready to go.
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