PERC Calculator - Pulmonary Embolism Rule-Out Criteria

Enter age, heart rate, oxygen saturation, and five yes/no findings to apply the 8-criterion PERC rule and see whether pulmonary embolism can be reasonably excluded without further testing.

Quick Facts

Who it's for
Low pretest-probability patients only
PERC is validated only after a clinician (or a score such as Wells) already places pretest probability of PE around 15% or lower.
Rule logic
All 8 criteria must be negative
A single positive criterion makes the result PERC-positive, meaning PE is not excluded on this basis alone.
Validation
~1% missed-PE rate when negative
Pooled validation studies report roughly a 1% false-negative rate for a negative PERC in the appropriate low-risk population.

Your Results

Calculated
PERC result
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Negative = all criteria clear
Criteria positive
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Count out of 8
Suggested next step
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Based on the rule outcome
Positive findings
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Which criteria triggered

Ready

Enter the patient's age, vitals, and history findings, then calculate the PERC result.

About the PERC rule

PERC (Pulmonary Embolism Rule-out Criteria) is a clinical decision rule used in emergency and urgent-care settings to identify patients who are unlikely to have a pulmonary embolism (PE) and can reasonably avoid further testing such as D-dimer or CT pulmonary angiography. It is intended only for patients a clinician has already judged to have a low pretest probability of PE - typically under about 15% by clinical gestalt or a validated score such as the Wells criteria.

The eight criteria

  • Age 50 years or older
  • Heart rate 100 beats per minute or higher
  • Oxygen saturation below 95% on room air
  • Unilateral leg swelling
  • Hemoptysis (coughing up blood)
  • Surgery or trauma requiring general anesthesia in the past 4 weeks
  • Prior pulmonary embolism or deep vein thrombosis
  • Current hormone use, including oral contraceptives, hormone replacement therapy, or other exogenous estrogen

How the rule is applied

If none of the 8 criteria are present, the patient is PERC-negative: the rule considers PE unlikely enough that no further PE-specific testing is needed on this basis. If even one criterion is present, the patient is PERC-positive, and PE is not excluded - the clinician continues with the standard diagnostic pathway, typically D-dimer testing followed by imaging if the D-dimer is elevated. The rule is a binary gate, not a probability score: it does not distinguish between one positive criterion and several.

When to consult a professional

This tool performs the standard PERC arithmetic for education and reference. It is not a diagnosis and does not replace clinical assessment. Pulmonary embolism can be serious and even life-threatening, so any concerning symptoms - chest pain, shortness of breath, leg swelling, or coughing up blood - need evaluation by a qualified healthcare professional, and the decision to pursue or forgo further testing rests with the treating clinician.

Frequently Asked Questions

What is the PERC rule and when is it used?
The PERC rule (Pulmonary Embolism Rule-out Criteria) is an 8-item checklist used only in patients a clinician has already judged to have a low pretest probability of pulmonary embolism. If all 8 criteria are negative, the rule considers further PE testing unnecessary; if any single criterion is positive, testing continues with the standard diagnostic pathway.
What are the 8 PERC criteria?
Age 50 or older; heart rate 100 beats per minute or higher; oxygen saturation below 95 percent on room air; unilateral leg swelling; hemoptysis (coughing up blood); surgery or trauma requiring general anesthesia in the past 4 weeks; a prior pulmonary embolism or deep vein thrombosis; and current hormone use such as oral contraceptives, hormone replacement therapy, or other exogenous estrogen.
How reliable is a negative PERC result?
In validation studies pooled across multiple cohorts, a negative PERC result in a patient already assessed as low pretest probability was associated with a missed pulmonary embolism rate of roughly 1 percent. The rule is only intended for patients whose overall clinical impression already places them in the low-probability group; it does not apply to moderate- or high-risk patients.

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