Pulse oximeter guides · Canada
Blood oxygen saturation (SpO₂) explained
A fingertip clip uses light to estimate oxygen saturation. Find out what the percentage describes, why a reading may be misleading and how to record a useful trend.
What the percentage estimates
Oxygen circulates in the blood bound mainly to haemoglobin. A pulse oximeter estimates the proportion of haemoglobin carrying oxygen in the blood flowing past its sensor. It displays that estimate as SpO₂.
Pulse rate has its own units, beats per minute. A single clip can display both values, so check the label before reading either number aloud or noting it in a log.
Why an estimate can be off
The optical sensor needs a usable signal. Motion, a poorly placed sensor, cold fingers and some nail coverings can affect the result. Health Canada also notes that pulse oximetry can overestimate blood oxygen saturation in people with darker skin.
Health care providers interpret the value with your symptoms and circumstances. A home reading is one piece of that picture.
What makes a trend useful
If your clinician has asked you to keep track, follow the same measurement instructions each time. Note the time, what you were doing, any symptoms and the value the device showed. Ask your clinician which changes to act on given your health and why you are monitoring.
When to ask for help
Health Canada identifies difficulty breathing, chest pain, changes in the colour of lips or nails and a falling reading among the signs to consider. Seek medical assessment for concerning symptoms. Avoid waiting for a second measurement to take serious symptoms seriously.