SpO2 — Blood Oxygen Saturation and What It Actually Tells You
Normal is 95–100%. What happens below that — and why your wearable data matters more than you think.
Track This Biomarker Free → ← All BiomarkersWhat Is SpO2?
SpO2 measures the percentage of hemoglobin molecules carrying oxygen in the bloodstream. Consumer wearables use photoplethysmography to estimate this via light absorption. Sustained readings below 94% indicate hypoxemia. Nocturnal dips below 88% are diagnostic for obstructive sleep apnea. COVID-19 research established that SpO2 declines are detectable via wearable days before clinical deterioration.
Why It Changes
- Altitude exposure above 8,000 feet
- Sleep apnea — nocturnal SpO2 dips during breathing cessation
- Respiratory illness — COVID-19, pneumonia, bronchitis
- Anemia — low hemoglobin reduces oxygen-carrying capacity
- Obesity — increases upper airway restriction risk
- Smoking — damages hemoglobin oxygen-binding capacity
How Hunuu Health Uses This Signal
Hunuu integrates SpO2 continuous monitoring from Apple Watch Series 6+, Oura Ring Gen 3, Fitbit Sense, and Garmin devices. Nocturnal SpO2 pattern analysis flags sleep apnea risk and respiratory health trends within the Respiratory health pillar.
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