PERC Calculator – Pulmonary Embolism Rule-Out Criteria

Written by Great Medico

Updated September 24, 2026 •2 min read

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A clinical score can look authoritative even when its assumptions are hidden. PERC Calculator – Pulmonary Embolism Rule-Out Criteria makes the calculation explicit so the number can be interpreted in the right cardiovascular context.

What this calculator does

PERC Calculator – Pulmonary Embolism Rule-Out Criteria uses Age ≥ 50 years, Heart rate ≥ 100 bpm, Oxygen saturation < 95%, Unilateral leg swelling, Hemoptysis, Surgery/trauma in previous 4 weeks, Prior PE/DVT, and Estrogen use to calculate PERC result. It is built around the exact fields displayed in this plugin rather than a generic version of the topic. Cardiovascular formulas are sensitive to measurement technique and clinical context. A mathematically correct output can still be misleading if the input was obtained under a different physiologic condition, with a different assay, or outside the population for which the score was developed.

How to use it

Complete the requested fields, including Age ≥ 50 years, Heart rate ≥ 100 bpm, Oxygen saturation < 95%, Unilateral leg swelling, Hemoptysis, and Surgery/trauma in previous 4 weeks, then finish the remaining items shown in the calculator. Confirm that each yes/no, category, date, or score option is applied exactly as labeled. When the formula combines measurements, use values obtained under the same assessment or physiologic conditions whenever possible.

How the calculation works

PERC contains eight yes/no exclusion criteria: age at least 50, heart rate at least 100, oxygen saturation below 95%, unilateral leg swelling, hemoptysis, recent surgery/trauma, previous PE/DVT, and estrogen use. The calculator counts positive criteria. Zero positives is labeled PERC negative; any positive criterion makes the rule positive.

Example

Using the sample values prefilled in this calculator, the primary result is 0 positive criteria (PERC negative). This worked example shows how the plugin’s own default inputs flow through the implemented method; replace them with the correct patient, laboratory, imaging, or personal values before interpreting a result.

How to interpret the result

Zero positive criteria is “PERC negative.” That result is meaningful only after a low pretest probability has already been established clinically. One or more positives means PERC cannot rule out PE; it does not mean pulmonary embolism is present.

Limitations and notes

PERC is not a general pulmonary-embolism screening test. It is intended only when a clinician has already judged the patient to have a low pretest probability of PE; using PERC in moderate- or high-risk patients can miss clinically important disease.