PERC rule (PE rule-out)
Rule-out criteria for PE in low pre-test probability.
What it is for
When clinical gestalt is low-risk: if ALL 8 criteria are negative, PE is excluded without D-dimer.
Use the working calculator
The working PERC rule (PE rule-out) calculator is on our calculators page. It is free and needs no account. Enter the values and it shows the result with the reading that goes with it.
The calculators are free. The trial opens the protocols and pathways they link to.What you enter
The calculator asks for 8 items.
- Age ≥ 50 (1 point)
- HR ≥ 100 (1 point)
- SpO₂ < 95% on room air (1 point)
- Haemoptysis (1 point)
- Oestrogen use (COC / HRT) (1 point)
- Prior DVT / PE (1 point)
- Recent surgery / trauma (≤ 4 weeks, needing GA) (1 point)
- Unilateral leg swelling (1 point)
How the result is read
The result is shown as PERC positive items, out of a maximum of 8.
The calculator reads each total as follows. Where a single answer changes the reading (for example sex, age or one extreme value), the working calculator says so.
| Total | Band | What the calculator says |
|---|---|---|
| 0 | PERC negative | In a low-risk patient, PE is excluded — no D-dimer needed. ALL 8 criteria absent + low clinical gestalt → < 2% PE risk. |
| 1 to 8 | PERC positive | Cannot exclude PE on PERC — proceed to Wells + D-dimer / imaging (NICE NG158). One or more criteria present. |
Sources
These are the sources the calculator cites. Check the current version before relying on a threshold.
Related
For qualified clinicians. A score supports a clinical decision and does not make it: check the inputs, read the cited source, and use the tools in your clinical system for patient care where one is provided.