PERC Rule, Well’s Critera
both are clinical decision rules used to identify patients low-risk for PE
breakdown of each rule set below, but here are some common themes in both rule sets for low-risk patients:
- HR <100
- No prior history of DVT/PE
- No recent trauma/immobilization/surgery
- No hemoptysis
- No clinical signs/symptoms of DVT (e.g. unilateral leg swelling)
there’s what you learned in medical school, coming back in actual clinical practice

So what else does Well’s Criteria look at?
- your clinical suspicion: asks if PE is tops on your differential
- cancer history: treatment within 6 months, or palliative
if you have NONE of these, plus none of the common list from above, then you’re low risk for PE (1.3%)
So what else does the PERC rule lookat?
- age: <50 (younger is better, apparently)
- hypoxia: room air 02 sat >94%
- estrogen: no exogenous estrogen (e.g. OCPs) is lower risk
if these 3 things, + the common 5 from above, are negative = low risk
may miss 1-2% of PEs, but suggested these would be low mortality/low clot burden patients
10-SECOND TAKEAWAY:
- clinical decision rules are low-risk, not NO risk
- accept some tiny risk of missing something when you use these, at the benefit of not irradiating everyone
- good luck
References: PERC rule MDCalc.com; Well’s Criteria MDCalc.com; picture
Tags: pulm