Wells Score for PE Calculator
Calculate the Wells Score for pulmonary embolism probability. Summarizes the standard 7 criteria into low, moderate, or high pretest-probability bands.
PERC Rule Calculator
Review the Pulmonary Embolism Rule-Out Criteria (PERC) and see whether all eight bedside criteria are absent in a low-risk worksheet setting.
⚠️ Reference Note: PERC was studied as a low-pretest-probability worksheet. This page summarizes the 8 criteria only; it does not determine testing, imaging, or diagnosis outside that low-risk context.
ℹ️ Prerequisite: PERC is intended for settings where clinician pre-test probability is already low (commonly described as under 15%). Outside that use setting, the worksheet becomes much less informative.
PERC Rule
All Criteria Absent
This matches the original low-risk PERC-negative worksheet pattern
Published miss rates were low when PERC was applied correctly to low-risk patients
PERC Criteria Status — all 8 must be absent for the classic low-risk negative pattern
✅ABSENT
Age ≥50
Patient is 50 years or older
✅ABSENT
Heart rate ≥100
Tachycardia at rest
✅ABSENT
O₂ sat <95% on room air
Pulse oximetry low on ambient air
✅ABSENT
Hemoptysis
Coughing up blood
✅ABSENT
Estrogen use
OCP, HRT, tamoxifen, or other estrogen use
✅ABSENT
Prior DVT or PE
History of venous thromboembolism
✅ABSENT
Recent surgery or trauma (within 4 weeks)
Required general anesthesia or hospitalization
✅ABSENT
Unilateral leg swelling
Asymmetric calf or thigh swelling
PERC Pattern⧉
All criteria absent
Matches the classic PERC-negative low-risk worksheet pattern
Criteria Present⧉
0 / 8
All 8 must be absent for the classic PERC-negative pattern
Worksheet Meaning⧉
Low-risk negative pattern only
This page does not determine testing or imaging
Pre-Test Requirement⧉
Low (<15%)
PERC only valid at low clinical suspicion
Published Miss-Rate Context⧉
<2%
From low-risk validation settings only
Published Sensitivity⧉
97.4%
Reported when PERC is applied correctly to low-risk patients
| Pre-Test Probability | How PERC Was Studied | Worksheet Context |
|---|---|---|
| Low (<15%) | Original low-risk validation setting | PERC is most interpretable here |
| Moderate (15-40%) | Outside the original low-risk use setting | PERC becomes less reliable as a stand-alone screen |
| High (>40%) | Outside the original low-risk use setting | PERC should not be treated as a stand-alone exclusion tool |
| PERC Criterion | Rationale |
|---|---|
| Age ≥50 | PE incidence increases with age |
| HR ≥100 | Tachycardia from V/Q mismatch |
| SpO₂ <95% | Hypoxemia suggests shunt/dead space |
| Hemoptysis | Pulmonary infarction sign |
| Estrogen use | Hypercoagulable state from estrogen |
| Prior DVT/PE | Recurrence risk 5-10% per year |
| Surgery/trauma | Virchow triad: stasis + injury |
| Leg swelling | Suggests concurrent DVT |
Planning notes, formulas, and examples
About the PERC Rule Calculator
The PERC (Pulmonary Embolism Rule-Out Criteria) rule is an 8-item bedside tool used in low-risk pulmonary embolism assessment. Developed by Kline et al. and later validated in emergency medicine studies, it is designed to identify the subset of patients whose overall profile is low enough that additional testing may be avoidable in some workflows.
This calculator keeps the eight criteria visible and simply shows whether the worksheet is all-negative or not. It does not determine a full PE workup on its own, and it should be interpreted only after low pre-test probability has already been established.
When This Page Helps
PERC is useful because it gives a structured yes/no checklist for a low-risk PE worksheet. It can help show whether the bedside criteria are fully absent rather than relying on memory or an informal impression.
That makes it most useful as a reference aid when discussing a low-risk presentation, not as a stand-alone imaging or treatment algorithm.
How to Use the Inputs
- First decide whether the case is truly low pre-test probability.
- Review each of the 8 PERC criteria.
- If all 8 criteria are absent, the worksheet is PERC negative.
- If any criterion is present, the worksheet is PERC positive.
- Use the result as part of the broader low-risk clinical context rather than as a stand-alone workup engine.
Formula used
PERC Rule — 8 Binary Criteria (all must be absent for an all-negative worksheet):
1. Age ≥50
2. Heart rate ≥100 bpm
3. SpO2 <95% on room air
4. Hemoptysis
5. Estrogen use
6. Prior DVT or PE
7. Recent surgery or trauma
8. Unilateral leg swelling
All absent = PERC negative
Any present = PERC positiveExample Calculation
Result: PERC Negative — all 8 criteria absent
A 38-year-old with chest pain but otherwise low-risk features has all 8 PERC criteria absent. In a true low pre-test probability setting, that pattern is the all-negative PERC profile commonly referenced in emergency medicine.
Tips & Best Practices
- Use PERC only after low pre-test probability is already established.
- Keep the eight criteria visible so it is clear which one changed the worksheet from negative to positive.
- A positive PERC result does not diagnose PE; it only means the all-negative pattern is not present.
- This page is best used as a documentation and reference aid rather than a pathway engine.
What PERC Adds
PERC is useful because it turns eight bedside yes/no items into a single all-negative or not-all-negative profile. That can help low-risk PE discussions stay structured instead of relying on memory alone.
Why Low-Risk Context Matters
The rule is intended only for already low-risk presentations. Outside that setting, the same eight criteria do not carry the same meaning, which is why this page should be treated as a worksheet and not as a stand-alone pathway engine.
Common Pitfalls
The most common problems are applying PERC outside low-risk settings, overlooking estrogen exposure, or forgetting that a positive PERC result does not diagnose PE. The page is most useful when it is used simply to document which of the eight criteria are present.
Sources & Methodology
Last updated:
Methodology
This calculator applies the eight Pulmonary Embolism Rule-Out Criteria exactly as a bedside exclusion rule, not as a stand-alone probability score. The page assumes the rule is being used only after the clinician has already judged the patient to have a low pre-test probability of PE. If all eight criteria are absent, the result is treated as PERC negative; if any criterion is present, the page directs the user back into the usual D-dimer or imaging pathway rather than claiming PE is likely.
The output should not be used in patients outside the rule's intended setting, such as moderate- or high-suspicion presentations, pregnancy, or inpatient populations. It is a structured way to avoid unnecessary D-dimer testing in carefully selected low-risk patients, not a replacement for the broader diagnostic algorithm.
Sources
- Prospective multicenter evaluation of the pulmonary embolism rule-out criteria (PubMed / Journal of Thrombosis and Haemostasis)
- Effect of the Pulmonary Embolism Rule-Out Criteria on Subsequent Thromboembolic Events Among Low-Risk Emergency Department Patients: The PROPER Randomized Clinical Trial (PubMed / JAMA) — Randomized trial evaluating the PERC strategy in low-risk emergency-department patients.
Frequently Asked Questions
If any PERC criterion is present, the worksheet is PERC positive. That does not diagnose PE; it only means the case no longer fits an all-negative PERC profile.
Pregnancy has separate physiologic considerations and is generally discussed using different diagnostic frameworks. This worksheet should not be treated as a stand-alone pregnancy pathway.
It means the broader clinical picture already suggests a low likelihood of PE before PERC is applied. PERC is intended only in that low-risk setting.
Wells and Geneva are broader pre-test probability tools, while PERC is an all-or-none bedside checklist intended for already low-risk settings.
No. It is best used as a bedside reference aid after low pre-test probability has already been established. The broader workup still depends on the full clinical context.
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