PERC Rule Calculator

Pulmonary embolism rule-out criteria

Review all eight PERC criteria

Enter the three measured values and mark each clinical finding. Every positive criterion counts once; only zero positive criteria is PERC-negative.

Worked example values are loadedAge 49, pulse 99 bpm, room-air oxygen saturation 95%, and all five findings set to No produce the example result shown here. This is a demonstration, not a patient conclusion. Changing any value clears the result and requires the applicability gate to be confirmed again.

Applicability gate

Confirm before using PERC

Worked example: clinician applicability is assumed.This checked gate belongs only to the worked example. A qualified clinician has already assessed an adult with suspected PE as low risk, confirmed PERC is appropriate, and confirmed a nonpregnant clinical context.

Criteria completionAnswer every item before calculating.

8/8

Vitals

Enter measured values

AgeAge ≥ 50 yearsyearsCompleted age; 50 or older makes this item positive.Negative · 0PulsePulse ≥ 100 beats/minbpmUse the pulse observed for this clinical assessment.Negative · 0Room-air oxygen saturationRoom-air oxygen saturation < 95%%Do not substitute a reading taken on supplemental oxygen.Negative · 0

Symptoms & exam

Mark present or absent

Unilateral leg swelling

Clinician-assessed swelling affecting one leg.

Hemoptysis

Current coughing up blood in this encounter.

History & exposures

Complete the remaining criteria

Recent qualifying surgery or trauma

Surgery or trauma requiring hospitalization within the previous four weeks.

Prior pulmonary embolism or DVT

Any clinician-confirmed prior PE or deep-vein thrombosis.

Estrogen use

Current exogenous estrogen exposure under the local protocol.

Worked example result

PERC-negative

0of 8 positive

In this clinician-confirmed low-risk context, a PERC-negative result supports ruling out PE without additional PE testing; it does not exclude other causes of symptoms.

A negative PERC result does not diagnose or guarantee that PE is absent.It does not replace examination, local protocol, clinician judgment, or determine testing or treatment by itself.

No positive PERC criteria

Eight-item review

8/8 checked

Age ≥50 yearsEntered: 49
Negative
Pulse ≥100 beats/minEntered: 99
Negative
Room-air oxygen saturation <95%Entered: 95
Negative
Unilateral leg swellingEntered: no
Negative
HemoptysisEntered: no
Negative
Surgery/trauma requiring hospitalization within 4 weeksEntered: no
Negative
Prior PE or DVTEntered: no
Negative
Estrogen useEntered: no
Negative

Emergency rule-out boundary

Use PERC only after a clinician establishes a low-risk PE context

PERC is an eight-item pulmonary embolism rule-out rule, not a symptom checker. Its safe starting point is a qualified clinician's prior judgment that an adult with suspected PE is already in an appropriately low-risk population.

Side-by-side guide · Emergency rule-out boundary

Zero positive PERC items does not mean zero PE probability

Entry gate: Clinician-defined low risk
Items: 8 unweighted criteria
Negative state: 0 positive items

PERC-negative
Exactly zero positive criteria in the validated low-risk context produces the rule's negative state. It is not a percentage, a diagnosis, or proof that embolism is impossible.
Any positive item
A count from one through eight means PERC is not negative. The count does not grade PE severity and does not itself choose D-dimer testing, imaging, observation, or treatment.
Different embolic framework
The CHA2DS2-VASc component worksheet concerns thromboembolic risk in established atrial fibrillation; it cannot rule out an acute pulmonary embolism.

Use PERC only after a clinician establishes a low-risk PE context: PERC is an eight-item pulmonary embolism rule-out rule, not a symptom checker. Its safe starting point is a qualified clinician's prior judgment that an adult with suspected PE is already in an appropriately low-risk population.

PERC begins after low-risk judgment, never before it

The original prospective evaluation enrolled emergency-department patients whose treating clinician had a low suspicion for pulmonary embolism, described as gestalt below 15%. ACEP supports PERC for adults already determined to be low risk; evidence is insufficient for using it to rescue a moderate- or high-risk presentation. The calculator therefore demands that clinical gate before counting anything.

PERC does not decide whether chest pain, shortness of breath, fainting, tachycardia, pregnancy-related symptoms, or leg findings represent PE. It also does not replace the different preoperative task answered by the original Lee RCRI worksheet. Starting with the wrong population invalidates otherwise perfect arithmetic.

Three cutoffs and five histories make the eight PERC stops

Each positive item counts once; there are no weights or partial points.

Age at least 50 years, pulse at least 100 beats per minute, or room-air oxygen saturation below 95% each makes its numeric criterion positive.
Unilateral leg swelling and hemoptysis are separate clinical findings, not values that the calculator can infer from free text or a photo.
Surgery or trauma requiring hospitalization within the prior four weeks follows the original study wording; a local protocol may define its operational item differently.
Prior pulmonary embolism or deep-vein thrombosis and estrogen use complete the list. All eight entries must be known rather than guessed.

Zero positive PERC items does not mean zero PE probability

PERC-negative

Exactly zero positive criteria in the validated low-risk context produces the rule's negative state. It is not a percentage, a diagnosis, or proof that embolism is impossible.

Any positive item

A count from one through eight means PERC is not negative. The count does not grade PE severity and does not itself choose D-dimer testing, imaging, observation, or treatment.

Different embolic framework

The CHA2DS2-VASc component worksheet concerns thromboembolic risk in established atrial fibrillation; it cannot rule out an acute pulmonary embolism.

Urgent symptoms outrank an online PERC count

Seek assessment
New or worsening breathing difficulty, chest pain, fainting, coughing blood, low oxygen readings, or one-sided leg swelling warrants prompt professional evaluation; call emergency services for severe or life-threatening symptoms.
Preserve the clinical context
Tell the clinician about pregnancy or postpartum status, recent hospitalization, cancer, immobility, prior clots, hormones, and anticoagulants. A web form cannot adjudicate exclusions or local prevalence.
Keep scores in their lanes
If the question is long-term atherosclerotic prevention rather than acute PE, the historical ASCVD PCE page addresses that separate model and carries its own limitations.

The PERC screen cannot diagnose, test, or treat pulmonary embolism

Do not use this page to reassure yourself at home, delay emergency care, stop anticoagulation, or decide against clinician-recommended testing. It gives only a transparent item count after the required gate. A qualified clinician, examination, local diagnostic pathway, and patient-specific judgment control the decision.

Important limitations

PERC Rule Calculator returns PERC positive item count, PERC negative, and applicability gate only for the stated population, method, and source period. It is an informational calculation rather than a diagnosis, treatment plan, dosing instruction, exposure assessment, or individualized clinical recommendation.

This formula passed its registered engineering tests and is published under an explicit site-owner policy authorization. No independent expert, QA, editorial, legal, or third-party review is claimed. Verify consequential results with a qualified professional.

This subject may affect health, finance, tax, legal, or other consequential decisions. It has not received an independent domain-expert review; consult a qualified professional before relying on it.

Emergency rule-out boundary

Use PERC only after a clinician establishes a low-risk PE context

Side-by-side guide · Emergency rule-out boundary

Zero positive PERC items does not mean zero PE probability

Entry gate: Clinician-defined low risk
Items: 8 unweighted criteria
Negative state: 0 positive items

PERC-negative
Exactly zero positive criteria in the validated low-risk context produces the rule's negative state. It is not a percentage, a diagnosis, or proof that embolism is impossible.
Any positive item
A count from one through eight means PERC is not negative. The count does not grade PE severity and does not itself choose D-dimer testing, imaging, observation, or treatment.
Different embolic framework
The CHA2DS2-VASc component worksheet concerns thromboembolic risk in established atrial fibrillation; it cannot rule out an acute pulmonary embolism.

PERC begins after low-risk judgment, never before it

Three cutoffs and five histories make the eight PERC stops

Each positive item counts once; there are no weights or partial points.

Age at least 50 years, pulse at least 100 beats per minute, or room-air oxygen saturation below 95% each makes its numeric criterion positive.
Unilateral leg swelling and hemoptysis are separate clinical findings, not values that the calculator can infer from free text or a photo.
Surgery or trauma requiring hospitalization within the prior four weeks follows the original study wording; a local protocol may define its operational item differently.
Prior pulmonary embolism or deep-vein thrombosis and estrogen use complete the list. All eight entries must be known rather than guessed.

Zero positive PERC items does not mean zero PE probability

PERC-negative

Exactly zero positive criteria in the validated low-risk context produces the rule's negative state. It is not a percentage, a diagnosis, or proof that embolism is impossible.

Any positive item

A count from one through eight means PERC is not negative. The count does not grade PE severity and does not itself choose D-dimer testing, imaging, observation, or treatment.

Different embolic framework

The CHA2DS2-VASc component worksheet concerns thromboembolic risk in established atrial fibrillation; it cannot rule out an acute pulmonary embolism.

Urgent symptoms outrank an online PERC count

Seek assessment
New or worsening breathing difficulty, chest pain, fainting, coughing blood, low oxygen readings, or one-sided leg swelling warrants prompt professional evaluation; call emergency services for severe or life-threatening symptoms.
Preserve the clinical context
Tell the clinician about pregnancy or postpartum status, recent hospitalization, cancer, immobility, prior clots, hormones, and anticoagulants. A web form cannot adjudicate exclusions or local prevalence.
Keep scores in their lanes
If the question is long-term atherosclerotic prevention rather than acute PE, the historical ASCVD PCE page addresses that separate model and carries its own limitations.