What is the PERC Rule?

PERC is a set of 8 criteria that, if ALL are negative in a LOW pre-test probability patient, allows clinicians to rule out PE without any further testing (no D-dimer, no CT). It has a sensitivity >97% and a false-negative rate <2% when applied correctly.

When should I use PERC?

PERC should ONLY be applied when clinical gestalt or Wells Score indicates LOW pre-test probability (<15%). It should NOT be used for moderate or high pre-test probability patients. If any single PERC criterion is positive, proceed with D-dimer testing.

What if the patient fails PERC?

If any criterion is positive, PERC cannot rule out PE. Proceed with D-dimer testing. If D-dimer is positive, CT pulmonary angiography is typically indicated. Follow the standard Wells Score → D-dimer → CTPA pathway.

Why is PERC important?

D-dimer testing in low-risk patients often yields false positives, leading to unnecessary CT scans with radiation exposure, contrast risks, and incidental findings. PERC reduces overtesting by ~20% in low-risk patients without missing clinically significant PE.

Online Medical Tools — PERC Rule

Printed on 2/13/2026

For informational purposes only. This is not medical advice.

Emergency

PERC Rule

The Pulmonary Embolism Rule-out Criteria (PERC) is a clinical decision tool designed to identify patients in whom pulmonary embolism can be safely excluded without D-dimer testing. If a clinician's pre-test probability is low AND all eight PERC criteria are negative, PE can be ruled out without further testing. This reduces unnecessary D-dimers, CT scans, and radiation exposure.

Compare with Wells Score (PE)

Formula: All 8 criteria must be negative to rule out PE (binary yes/no)

Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.