PERC Calculator

The PERC Calculator applies the Pulmonary Embolism Rule-out Criteria to help clinicians determine if further PE workup can be safely avoided. Enter the patient's age, heart rate, and O₂ saturation, then check the relevant clinical flags — hemoptysis, estrogen use, prior DVT/PE, unilateral leg swelling, and recent surgery or trauma. The tool returns a PERC result (positive or negative) along with a clear interpretation of whether pulmonary embolism can be ruled out based on the criteria.

years

Patient must be under 50 for this criterion to be negative.

bpm

Heart rate ≥100 bpm is a positive PERC criterion.

%

O₂ sat <95% on room air is a positive PERC criterion.

Any blood in cough/sputum?

Includes OCP, HRT, or other estrogen therapy.

Prior history of venous thromboembolism.

Swelling in one leg only, suggesting DVT.

Any surgery or significant trauma within the previous 4 weeks.

Results

PERC Result

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Criteria Met

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Interpretation

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PERC Criteria: Met vs. Not Met

Results Table

Frequently Asked Questions

What is the PERC rule and what does it stand for?

PERC stands for Pulmonary Embolism Rule-out Criteria. It is a set of eight clinical criteria used in emergency medicine to identify patients with a low pre-test probability of pulmonary embolism who do not require further diagnostic workup such as D-dimer testing or CT pulmonary angiography.

When can PE be ruled out using the PERC rule?

PE can be ruled out when a patient meets ALL of the following: age under 50, heart rate below 100 bpm, O₂ saturation ≥95% on room air, no hemoptysis, no estrogen use, no prior DVT or PE, no unilateral leg swelling, and no surgery or trauma in the past 4 weeks. Additionally, the clinician's pre-test probability of PE must be below 15%.

What pre-test probability is required before applying the PERC rule?

The PERC rule should only be applied when the clinician's gestalt (pre-test probability) is low — generally defined as less than 15%. Applying PERC to intermediate or high-risk patients is inappropriate and potentially dangerous.

What does a PERC-positive result mean?

A PERC-positive result means the patient meets one or more of the eight criteria. This does not confirm PE, but it indicates that further evaluation — such as D-dimer testing or imaging — is warranted before PE can be excluded.

What are the limitations of the PERC rule?

The PERC rule is not a standalone diagnostic tool and must be used alongside clinical judgment. It should not be applied to patients with intermediate or high pre-test probability of PE. It also does not account for all risk factors and is not validated in all patient populations, including pregnant patients.

How does the PERC rule relate to D-dimer testing?

If a patient is PERC-negative (all eight criteria are absent) and pre-test probability is low, D-dimer testing can be safely avoided, reducing unnecessary costs and follow-up imaging. If any PERC criterion is positive, D-dimer or imaging may be the next step depending on clinical risk stratification.

How does the PERC rule compare to the Wells score for PE?

The Wells score quantifies pre-test probability of PE using clinical features and is used to stratify patients into low, moderate, or high risk groups. The PERC rule is then applied to low-risk Wells patients to determine if no further testing is needed. The two tools are complementary — Wells first, then PERC.

Is the PERC calculator a substitute for clinical judgment?

No. The PERC calculator is a clinical decision support tool and should never replace thorough clinical assessment by a qualified healthcare provider. Always integrate the PERC result with the full clinical picture, patient history, and physician expertise.

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