🫁 PERC Rule (PE Rule-out Criteria)
Apply the PERC rule to exclude pulmonary embolism without D-dimer in low-risk patients.
Only valid in low pre-test-probability patients.
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When to use
Rule out PE when clinical pre-test probability is already low.
How it works
Eight criteria (age ≥ 50, HR ≥ 100, SpO₂ < 95%, haemoptysis, oestrogen, prior DVT/PE, unilateral leg swelling, surgery/trauma ≤ 4 weeks). If all are negative, PE is excluded.
Key points
- Only valid in low pre-test-probability patients.
- Any positive criterion means PERC fails — proceed with workup.
- Avoids unnecessary D-dimer testing.
References
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Age ≥ 50 | No |
|---|---|
| Heart rate ≥ 100 | No |
| SpO₂ < 95% | No |
| Haemoptysis | No |
| Oestrogen use | No |
| Prior DVT/PE | No |
| Unilateral leg swelling | No |
| Surgery/trauma ≤ 4 weeks (needing hospitalisation) | No |
→PERCAll negative
- Interpretation：In a low pre-test-probability patient, PE can be excluded without D-dimer.
| Age ≥ 50 | Yes |
|---|---|
| Heart rate ≥ 100 | Yes |
| SpO₂ < 95% | Yes |
| Haemoptysis | Yes |
| Oestrogen use | Yes |
| Prior DVT/PE | Yes |
| Unilateral leg swelling | Yes |
| Surgery/trauma ≤ 4 weeks (needing hospitalisation) | Yes |
→PERC8 positive
- Interpretation：PERC not satisfied — proceed with D-dimer/imaging per pathway.
Frequently asked questions
- What is PERC Rule (PE Rule-out Criteria)?
- Apply the PERC rule to exclude pulmonary embolism without D-dimer in low-risk patients.
- How is PERC Rule (PE Rule-out Criteria) calculated? What is the core formula?
- Eight criteria (age ≥ 50, HR ≥ 100, SpO₂ < 95%, haemoptysis, oestrogen, prior DVT/PE, unilateral leg swelling, surgery/trauma ≤ 4 weeks). If all are negative, PE is excluded.
- When is PERC Rule (PE Rule-out Criteria) used?
- Rule out PE when clinical pre-test probability is already low.
- What are the key clinical points for PERC Rule (PE Rule-out Criteria)?
- Only valid in low pre-test-probability patients. Any positive criterion means PERC fails — proceed with workup. Avoids unnecessary D-dimer testing.
- What are the limits and cautions when using PERC Rule (PE Rule-out Criteria)?
- For licensed clinicians and clinical researchers. Interpret results with history, investigations and local protocols; not a diagnosis or prescription, and not a substitute for multidisciplinary decision-making or local guidelines.
- How is PERC Rule (PE Rule-out Criteria) calculated in practice? Can you show a worked example?
- Inputs: Age ≥ 50 No, Heart rate ≥ 100 No, SpO₂ < 95% No, Haemoptysis No, Oestrogen use No, Prior DVT/PE No, Unilateral leg swelling No, Surgery/trauma ≤ 4 weeks (needing hospitalisation) No → Result: PERC All negative（Interpretation: In a low pre-test-probability patient, PE can be excluded without D-dimer.） Inputs: Age ≥ 50 Yes, Heart rate ≥ 100 Yes, SpO₂ < 95% Yes, Haemoptysis Yes, Oestrogen use Yes, Prior DVT/PE Yes, Unilateral leg swelling Yes, Surgery/trauma ≤ 4 weeks (needing hospitalisation) Yes → Result: PERC 8 positive（Interpretation: PERC not satisfied — proceed with D-dimer/imaging per pathway.）