Blood Oxygen (SpO2)

% saturation

The percentage of hemoglobin in the bloodstream that is saturated with oxygen. Higher numbers indicate higher levels of oxygen in the blood.

Typical optimal range 95% - 100%

Population median 97%

Sustained readings below 95% at rest are worth a conversation with a clinician.

Key factors

Sleeping on your back lowers overnight saturation compared with side sleeping for sleep-disordered populations.
Asthma, COPD, and other lung conditions lower it.
Altitude lowers blood oxygen until acclimatization occurs.
Sleep apnea causes repeated overnight drops.
Nasal congestion, smoking, and respiratory illness reduce saturation.
Cold hands and a loose device fit can lower the reading itself.

Peer-reviewed sources supporting the key factors, contributing factors, and typical optimal range shown above.

Rodríguez-Molinero A, Narvaiza L, Ruiz J, Gálvez-Barrón C. Normal respiratory rate and peripheral blood oxygen saturation in the elderly population. Journal of the American Geriatrics Society. 2013;61(12):2238–2240. doi.org/10.1111/jgs.12580
Jubran A. Pulse oximetry. Critical Care. 2015;19:272. doi.org/10.1186/s13054-015-0984-8
Luks AM, Swenson ER. Pulse oximetry at high altitude. High Altitude Medicine & Biology. 2011;12(2):109–119. doi.org/10.1089/ham.2011.0013
Joosten SA, O'Driscoll DM, Berger PJ, Hamilton GS. Supine position related obstructive sleep apnea in adults: pathogenesis and treatment. Sleep Medicine Reviews. 2014;18(1):7–17. doi.org/10.1016/j.smrv.2013.01.005

This guide is general information, not medical advice. Talk to your clinician about your own results.