PERC Rule

What This Calculator Measures

Determines whether pulmonary embolism can be safely ruled out in a patient with low pre-test probability, without D-dimer or imaging.

How to Use

1. Confirm the patient has a low pre-test probability of PE (e.g., Wells PE score below 4).
2. Assess each of the eight PERC criteria.
3. Select Yes for each criterion that is satisfied.
4. If all 8 are met, PE is considered ruled out.

Interpretation Guide

8/8 criteria met: PERC negative, PE can be ruled out without further testing. Fewer than 8/8: PERC positive, proceed with D-dimer and/or imaging.

Clinical Significance

The PERC rule safely reduces unnecessary D-dimer testing and CT pulmonary angiography in low-risk patients, lowering cost and radiation exposure without missing clinically significant PE.

When to Use

• Adult emergency patients with suspected PE and low pre-test probability
• Before ordering D-dimer or CT pulmonary angiography in low-risk patients
• To reduce unnecessary testing and radiation exposure

When Not to Use

• Patients with intermediate or high pre-test probability of PE
• Patients with signs of hemodynamic instability or shock
• Pregnant patients
• As a stand-alone rule-out in patients with a high-risk presentation

Limitations

• The rule only applies when pre-test probability is low; it does not replace clinical judgment.
• Original derivation excluded pregnant patients and children.
• A positive PERC does not diagnose PE; it only indicates further testing is warranted.

Worked Example

A 35-year-old woman with pleuritic chest pain has HR 88 bpm, SpO2 97% on room air, no hemoptysis, no estrogen use, no prior DVT/PE, no leg swelling, and no recent surgery or trauma.

All 8 PERC criteria met — PERC negative. PE can be considered ruled out without D-dimer or imaging given the low pre-test probability.

Evidence

Source

PERC Rule Derivation / Validation

Reference

Kline JA, 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.

Reviewed By

MedCalcHub Clinical Team

Version

1.0

Updated

2026-08

1. Kline JA, et al. J Thromb Haemost. 2004;2(8):1247-1255.
2. Kline JA, et al. Ann Emerg Med. 2004;44(5):490-502.

References

1. Kline JA, 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. (Original Derivation)
2. Kline JA, et al. Impact of a rapid rule-out protocol for pulmonary embolism on the rate of screening, missed cases, and pulmonary vascular imaging in an urban US emergency department. Ann Emerg Med. 2004;44(5):490-502. (Validation Study)

Frequently Asked Questions