“Normal SpO2 values are in the high or even mid- to low 90s,” says Atul Malhotra, M.D., a critical care pulmonologist and sleep medicine specialist at UC San Diego Health.

Low levels of blood oxygen, conversely, can lead to symptoms known as hypoxemia. A normal SpO2 reading is anything between 95% and 99%. It is more accurate to say that SpO2 is a measure of hemoglobin.