Rule out PE in low-risk patients. Free to use.
PERC Rule (Pulmonary Embolism Rule-out Criteria) is a validated clinical instrument used to assess rule out pe in low-risk patients. The instrument contains 8 items.
Source / attribution: Kline JA et al., J Thromb Haemost 2004
The instrument's primary construct — rule out pe in low-risk patients — is operationalized through a fixed set of items, each with a defined response format. This standardisation is what allows PERC Rule scores to be compared meaningfully across clinicians, sites, and studies.
Like all screening or assessment instruments, PERC Rule is a structured aid — not a diagnostic test in isolation. Results should be interpreted alongside history, examination, and clinical context. Where a score crosses an actionable threshold, the next step is typically a more detailed clinical evaluation rather than a definitive diagnosis.
Answer all 8 items below to see your PERC Rule score and interpretation.
All scoring runs in your browser. No data is sent anywhere — close the tab and the answers are gone.
PERC Rule uses weighted summation: each item carries a fixed weight that is added when the response indicates a positive finding.
Scoring notes: Apply only when pre-test probability is low. Educational use only.
The cutoffs below are drawn from the published validation literature. Always interpret in clinical context.
| Score range | Band | Interpretation |
|---|---|---|
| 0–0 | PE ruled out | PE ruled out — no further tests needed. |
| 1–8 | Cannot rule out PE | Cannot rule out by PERC alone — more testing needed. |
This is an illustrative walkthrough, not a real patient. Follow the same four steps with your own answers — or use the live calculator at the top of this page.
Mark each item Yes or No. Each "Yes" adds the item's weight; each "No" adds 0. The example below uses illustrative answers.
| # | Item | Example response | Score |
|---|---|---|---|
| 1 | Age ≥ 50 | Yes | 1 |
| 2 | HR ≥ 100 bpm | Yes | 1 |
| 3 | SaO2 < 95% on room air | Yes | 1 |
| 4 | Hemoptysis | No | 0 |
| 5 | Exogenous estrogen use | Yes | 1 |
| 6 | Prior DVT or PE | No | 0 |
| 7 | Recent surgery or trauma (≤ 4 weeks, requiring GA) | Yes | 1 |
| 8 | Unilateral leg swelling | No | 0 |
Add the weights from the items where you marked "Yes" (skip the "No" answers — they contribute 0).
1 + 1 + 1 + 0 + 1 + 0 + 1 + 0 = 5
Find the row in the interpretation table whose range contains your total:
Total = 5 falls between 1 and 8 → Cannot rule out PE
Cannot rule out PE. PERC fails — proceed with D-dimer or imaging based on Wells.
A score is one input alongside history and examination. PERC Rule supports clinical judgment — it does not replace it.
If PERC Rule doesn't fit your context, related instruments in pulmonology include:
| Scale | Measures | Items | Time |
|---|---|---|---|
| CURB-65 | 30-day mortality in community-acquired pneumonia | 5 | — |
| mMRC Dyspnea Scale | Functional impact of breathlessness | 1 | — |
| sPESI | 30-day mortality risk after acute PE | 6 | — |
| Wells Score (PE) | Pre-test probability of pulmonary embolism | 7 | — |
| APGAR Score | Rapid assessment of newborn at 1 and 5 min | 5 | — |
| ASA Physical Status | Pre-operative health status | 1 | — |
| CHA2DS2-VASc | Annual stroke risk in non-valvular atrial fibrillation | 8 | — |
| Glasgow Coma Scale | Level of consciousness after head injury | 3 | — |
PERC Rule (Pulmonary Embolism Rule-out Criteria) is a validated instrument that assesses rule out PE in low-risk patients. It is designed for clinicians, medical students, evidence-synthesis researchers. The 8 items are combined to produce a total score.
PERC Rule contains 8 items. Item scores are combined with weighted scoring to produce the total. Scores run from 0 to 8, grouped into 2 interpretation bands from ‘PE ruled out’ up to ‘Cannot rule out PE’.
On the PERC Rule (total score 0–8), scores of 1–8 fall in the ‘Cannot rule out PE’ band — interpreted as: Cannot rule out by PERC alone — more testing needed. The full ladder is: 0 — PE ruled out: PE ruled out — no further tests needed.; 1–8 — Cannot rule out PE: Cannot rule out by PERC alone — more testing needed. A higher score reflects a more severe presentation, and crossing a cutoff is a prompt to step up assessment or care — but these bands are screening thresholds, not diagnoses.
Scores of 0 fall in the ‘PE ruled out’ band: PE ruled out — no further tests needed. A low score is reassuring but does not by itself rule out the underlying condition — if symptoms or clinical suspicion persist, reassess over time or use a complementary evaluation rather than relying on the number alone.
Yes — PERC Rule is in the public domain and free for clinical, educational, and research use without permission. You can use this calculator and the scale itself freely; if you publish results or reproduce the scale, cite the original source paper.
Kline JA et al. J Thromb Haemost. 2004;2(8):1247-1255. This is the original publication for the PERC Rule — the reference to cite when reporting results.
No. PERC Rule is a structured assessment aid, not a diagnostic test. Its proper role is clinical assessment of rule out PE in low-risk patients — it standardizes assessment and flags who needs closer evaluation, but the result must be weighed alongside history, examination, and clinical context. When a score conflicts with your clinical impression, clinical judgment takes precedence; treatment decisions should never rest on a screening score alone.
PERC Rule is supported by the following peer-reviewed sources: