A good trend tool, not a precise instrument.
The FDA is explicit: real readings can run a few points off true oxygen saturation, with error sources including poor circulation, cold fingers, nail polish, movement, and darker skin pigmentation - the subject of an FDA safety communication. Sit still, warm your hands, remove polish, and watch the direction over time. And symptoms beat the device: serious breathlessness needs urgent care whatever the number says.
What to do
Common questions
How accurate is a pulse oximeter?
Accurate enough to follow a trend, not precise enough to treat any single number as gospel. Pulse oximeters estimate blood oxygen through light passed through your fingertip, and the FDA has been explicit about the limits: real readings can differ from true oxygen saturation by a few percentage points, with known error sources including poor circulation, cold fingers, nail polish, movement, and darker skin pigmentation - the FDA issued a safety communication about pigmentation-related accuracy concerns and has kept working the problem since. The practical rules: sit still, warm your hands, remove polish, take a few readings, and watch the direction over time rather than fixating on one figure. The clinical line that matters: symptoms beat the device - if you feel seriously short of breath, blue-lipped, or confused, you need urgent care whatever the oximeter says, and a persistently low reading without symptoms still warrants a same-day call. Pymander, a free AI doctor available 24/7 by text, can help you interpret a trend.