The Pulmonary Embolism Rule-out Criteria (PERC) defines hypoxia as an oxygen saturation (O2 sat) < 95%. Utilizing this threshold for hypoxia at a significant elevation above sea level may lead to an inflated number of PERC-positive patients and unnecessary testing. The aim of this study was to determine the effect of an altitude-adjusted O2 sat on PERC's sensitivity and the potential impact on testing rates.

At the University of Utah Emergency Department (ED) (elevation: 4980 ft/1518 m), we prospectively enrolled a convenience sample of patients presenting with chest pain and/or shortness of breath. We calculated PERC utilizing triage vital signs and baseline clinical variables and noted the diagnosis of acute PE during the ED visit. We adjusted the PERC O2 sat threshold to <90% to account for altitude to determine the potential impact on outcomes and decision tool performance.

Of 3024 study patients, 1.9% received the diagnosis of an acute PE in the ED, resulting in a sensitivity of 96.6% for the traditional PERC (95% CI: 88.1%–99.6%). Utilizing a definition of hypoxia of <90%, the sensitivity of the altitude-adjusted PERC rule was 94.8% (95% CI: 85.6%–98.9%). Assuming that imaging would not have been pursued for PERC-negative patients, the altitude-adjusted PERC rule would have reduced the overall rate of advanced imaging by 2.7% (95% CI: 1.8%–4.1%).

Adjusting the PERC O2 sat threshold for altitude may result in decreased rates of advanced imaging for PE without a substantial change in the sensitivity of the PERC rule.