Accuracy of pulse oximeters at low oxygen saturation This Safety Alert was updated and reissued on 11 January 2022 in light of new information. Please refer to Reissued: Accuracy of pulse oximeters at low oxygen saturation. Pulse oximeters may overestimate arterial oxygen saturation (SpO2) for patients with non-white skin when SpO2 falls below 90 per cent. This disparity widens as SpO2 falls, is more pronounced in individuals with darkly pigmented skin, and is likely to be clinically important below SpO2 80 per cent. Studies published in the mid-2000s1,2 investigated this phenomenon. A recent article in the Boston Review highlighted the significance of this in the context of patients with COVID-19 using pulse oximeters to monitor their oxygen saturation at home.