Which of the following is a PERC criterion?

• A. Age under 50
• B. Oxygen saturation ≥95%
• C. Presence of leg swelling
• D. Recent surgery within 1 month

Answer: (B)

PERC (Pulmonary Embolism Rule-out Criteria) is used to decide when PE can be ruled out in low-risk patients without imaging. A key item in this rule is oxygen saturation of 95% or higher, measured on room air. If a patient meets all PERC criteria, including O2 saturation ≥95%, PE can be considered unlikely enough to forego further testing.

Oxygen saturation ≥95% is the best answer here because it is the direct, objective sign of adequate oxygenation that PERC relies on to lower the likelihood of PE. The other options can appear in different versions of PERC or, in some cases, would actually disqualify using PERC (for example, leg swelling suggests possible DVT and is not a PERC criterion to rule out PE). Recent surgery within 1 month can be part of some PERC formulations, but the saturation criterion is the most consistently recognized and central measure in the rule.