Understanding blood oxygen levels and pulse oximeters
Fingertip pulse oximeters became a household item during the COVID-19 pandemic. They're useful, but only if you know what the number means and where it can mislead you.
What a pulse oximeter measures
The device shines light through your fingertip and estimates how much of the hemoglobin in your blood is carrying oxygen. The result is shown as SpO2, a percentage. It also shows your pulse rate.
What's normal?
- Most healthy people read 95% to 100% at rest.
- Some people with chronic lung disease normally run lower; their doctor will tell them their target range.
- Readings at higher altitude, or in a plane cabin, are often a few points lower.
Contact your doctor if your reading is consistently below the range they've given you, or below 95% if you haven't been given one. Call 911 if you have severe shortness of breath, chest pain, confusion, or bluish lips or face, whatever the number says.
Getting an accurate reading
- Sit still and rest for a few minutes first.
- Warm your hands; cold fingers give poor readings.
- Remove nail polish or acrylic nails from the finger you're using.
- Keep your hand at heart level and stay still.
- Wait for the number to settle, then note it.
Known limitations
- Skin pigmentation. The FDA has warned that pulse oximeters can be less accurate in people with darker skin and may overestimate oxygen levels. Pay attention to symptoms, not just the number.
- Carbon monoxide. Standard oximeters can't tell oxygen apart from carbon monoxide, so they can show a falsely normal reading in CO poisoning.
- Poor circulation, movement and bright light can all throw off readings.
- Over-the-counter devices sold for "wellness" aren't held to the same standards as prescription devices.
Trends beat single readings
One odd reading isn't a cause for panic. Recheck. If you're monitoring a condition, write down readings at the same times each day and share the pattern with your doctor.
How this connects to HBOT
A pulse oximeter measures oxygen carried by hemoglobin, which is already near full in healthy people. Hyperbaric oxygen mainly raises oxygen dissolved in plasma, which an oximeter doesn't measure. See How HBOT works.