What does a negative PERC rule mean?

If all 8 criteria are absent (PERC negative), the post-test probability of PE is below 2% in a patient with low pretest probability, and PE can be ruled out without further testing such as D-dimer or CT pulmonary angiography.

Can I use PERC in all patients with suspected PE?

No. PERC is only valid in patients who already have a LOW pretest probability of PE (typically determined by clinical gestalt or a Wells score ≤ 4). It should never be applied to intermediate- or high-risk patients.

What happens if one criterion is positive?

A single positive criterion makes PERC positive, meaning the rule cannot rule out PE. The next step is typically a high-sensitivity D-dimer test, and if elevated, CT pulmonary angiography.

What is the sensitivity and specificity of the PERC rule?

When applied correctly to low-pretest-probability patients, the PERC rule has a sensitivity of approximately 97% and a specificity of around 22%, with a miss rate under 2%.

Does this tool replace a physician's clinical judgment?

No. This calculator is for educational and reference purposes only. Clinical decisions must always be made by a qualified healthcare provider considering the full clinical picture.

PERC Rule

Check all 8 PERC criteria to rule out pulmonary embolism without further testing in low-risk patients.

PERC Criteria

Check every criterion that applies to the patient

Only use PERC in patients with low pretest probability of pulmonary embolism. This tool is for educational reference only — not a substitute for clinical judgment.

Age ≥ 50 years

Heart rate ≥ 100 bpm

O₂ saturation < 95% on room air

Unilateral leg swelling

Clinical evidence of deep vein thrombosis

Hemoptysis

Coughing up blood

Recent surgery or trauma

Within 4 weeks, requiring general anesthesia or hospital admission

Prior PE or DVT history

Previously diagnosed pulmonary embolism or deep vein thrombosis

Exogenous estrogen use

Oral contraceptives, hormone replacement therapy, or other estrogen-containing medications

Result

Criteria positive

0 / 8

PERC Negative

All 8 criteria are absent. In a patient with low pretest probability, PE can be ruled out without further testing (post-test probability < 2%).

Reference: Kline JA, Mitchell AM, Kabrhel C, Richman PB, Courtney DM. Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism. J Thromb Haemost. 2004;2(8):1247–1255.

Summary

The PERC (Pulmonary Embolism Rule-out Criteria) rule is a validated clinical decision tool used in emergency medicine to identify patients with suspected pulmonary embolism who are at very low risk and do not require further diagnostic workup. It was developed by Kline et al. and validated in multiple studies to safely exclude PE when all 8 criteria are met in patients with a low pretest probability. Using the PERC rule appropriately reduces unnecessary D-dimer testing and CT pulmonary angiography in low-risk patients.

How it works

Establish that the patient has a low pretest probability of PE (clinical gestalt or Wells score).
Evaluate each of the 8 PERC criteria for the patient.
If ALL 8 criteria are negative (no box checked), PE can be ruled out without further testing.
If ANY criterion is positive (one or more boxes checked), PERC is positive and further workup (D-dimer or CTPA) is required.
Document the result and proceed accordingly based on clinical judgment and institutional protocol.

Use cases

Emergency department evaluation of chest pain or dyspnea with low PE suspicion.
Avoiding unnecessary D-dimer tests and radiation from CT scans.
Rapid bedside risk stratification before ordering imaging.
Teaching clinical decision-making for medical students and residents.
Quality assurance reviews for appropriate PE workup in low-risk patients.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu