Pulmonary Embolus Rule-out Criteria (PERC)
A large US study reported that use of the PERC tool by a ‘board certified emergency department clinician’ in the assessment of patients at low risk of PE allowed re-stratification of some patients into a ‘no risk’ group where further investigation (including D-dimer) may not be needed11. A 2012 systematic review suggests that these patients have less than a 2% chance of having a PE12.
| All answers to the following questions must be yes: |
| Low risk by Gestalt or other criteria? |
| Age <50? |
| Pulse <100? |
| Oxygen saturations on room air >94%? |
| No unilateral leg swelling? |
| No haemoptysis? |
| No recent trauma or surgery? |
| No previous VTE? |
| No oral hormone use? |
The American College of Emergency Physicians13 has included the following level B recommendation in its 2018 clinical policy on acute venous thromboembolism.
Level B Recommendations
For patients who are at low risk for acute PE, use the Pulmonary Embolism Rule-out Criteria (PERC) to exclude the diagnosis without further diagnostic testing.
NICE guideline14 on the diagnosis of VTE suggest that in patients in whom the clinical suspicion of PE is low, ie; estimated to be less than 15% based on overall clinical impression, using PERC can be considered to help determine whether any further investigations are needed.
The use of PERC however is not included in their visual aid on the diagnostic work up of PE as the evidence to support is use is limited.
Nice suggest in low risk patients PERC may reduce the need for further testing and unnecessary anticoagulation.
Learning bite
The PERC tool may be useful for ruling out PE in a select cohort of patients, when used by experienced clinicians.