Oxygen Level (SpO2) Interpreter

SpO2 (peripheral oxygen saturation) measures the percentage of hemoglobin in your blood that is carrying oxygen. A pulse oximeter clips to your fingertip and uses light to estimate this value non-invasively.

SpO2 interpretation ranges (at or near sea level):

Two numbers in that table deserve naming rather than leaving as band edges. 90% is the usual clinical definition of hypoxemia, the point at which low blood oxygen stops being a statistical observation and becomes a diagnosis. 88% is the threshold used in the United States to qualify for home oxygen therapy, which is why it turns up constantly in discharge instructions. A reading that sits at 88 repeatedly is not borderline; it is the number the system is built around.

If you have a chronic lung condition, this table is the wrong one for you. People with advanced COPD (chronic obstructive pulmonary disease) often live steadily in the high 80s, and a target range of 88 to 92% is common because pushing their saturation higher can suppress the drive to breathe. What matters in that case is a change from your own baseline, not the distance from 95. Use the range your clinician gave you.

How pulse oximeters work: The device shines red and infrared light through your finger. Oxygenated hemoglobin absorbs more infrared light, while deoxygenated hemoglobin absorbs more red light. The ratio of absorption determines the SpO2 percentage.

Factors that can affect accuracy:

• Poor circulation or cold fingers can give falsely low readings.
• Dark nail polish (especially black, blue, or green) can interfere with the sensor.
• Bright ambient light can cause errors. Shield the sensor from direct sunlight.
• Carbon monoxide poisoning can give falsely high readings because the sensor cannot distinguish carboxyhemoglobin from oxyhemoglobin.
• Skin pigmentation may slightly affect accuracy in some devices.
• Movement or shivering reduces accuracy. Keep your hand still and warm.

Altitude and SpO2: At higher elevations lower air pressure means less available oxygen, so the whole scale shifts down. The calculator asks where you are and moves the bands with you, because applying the sea-level table in Denver or La Paz produces alarm over readings that are perfectly ordinary there.

One important exception to reading the table calmly: a newcomer who has just gained altitude is a different case from an acclimatised resident. Someone who flew into a mountain town yesterday, is reading low, and has a headache, nausea, or breathlessness at rest may be developing altitude sickness, where the answer is to go down rather than to look up what is normal at that elevation.

The relationship between SpO2 and PaO2: SpO2 and PaO2 (partial pressure of oxygen in arterial blood, measured in mmHg) follow the oxygen-hemoglobin dissociation curve, which is not linear:

Important disclaimer: This tool is for general educational reference only. It is not a substitute for professional medical advice, diagnosis, or treatment. If you have concerns about your oxygen levels, consult a healthcare provider.