Pulse oximeter accuracy: what your reading can—and cannot—tell you

A fingertip pulse oximeter displays a precise-looking number, but that number is an estimate. The device uses light to estimate oxygen saturation, often labeled SpO2, and may also display pulse rate. It is not a direct blood sample, a diagnosis, or proof that breathing is normal. Understanding its limits helps you keep a more useful record and avoid relying on a reassuring display when you feel unwell.

SpO2 and pulse are different readings

SpO2 is an estimate of the percentage of hemoglobin carrying oxygen. Pulse rate is the number of heartbeats per minute. Record them in separate fields and keep the labels and units: percent for oxygen saturation and bpm for pulse. If the screen has several numbers, consult the manual instead of guessing which is which.

The FDA distinguishes medical-purpose pulse oximeters from general wellness products. Not every device sold online has been evaluated for clinical use. Ask your provider whether home monitoring is appropriate for you and what type of device and monitoring plan it recommends.

Why a number may be less reliable

FDA and MedlinePlus describe factors that can affect readings. A single display cannot tell you whether all of those factors have been avoided. Follow the manufacturer's instructions about placement, waiting for a stable result, and how to recognize a poor signal.

• Movement or incorrect placement can interfere with a reading.
• Cold fingers or poor circulation can make measurements harder.
• Nail polish and artificial nails can affect some measurements.
• Skin pigmentation can affect accuracy; FDA highlights performance concerns across skin tones.

Skin tone: a limitation worth discussing

The FDA has raised concerns that pulse oximeters may perform differently across skin pigmentation. This can include a reading that looks more reassuring than the person's actual oxygen level. There is no universal home correction formula to apply to the display. Do not add or subtract a percentage on your own; discuss the device's limits with your care team.

A seemingly normal result does not cancel serious symptoms. FDA advises considering how you feel and not relying only on the device. This is particularly important if breathing is worsening or the reading does not match your experience.

What to put in an oxygen-reading log

• Date, time, displayed SpO2 percentage, and pulse if shown.
• Device name or model when known, especially if switching devices.
• How you felt: breathing changes, chest discomfort, or other symptoms, in your own words.
• Relevant measurement context, such as movement, cold hands, or an unstable display.

Use your care plan, not a universal cutoff

Ask your clinician what readings and changes matter in your situation, when to repeat a measurement, and when to contact the team. A personal plan may take account of your health conditions and circumstances. Do not change prescribed oxygen settings or medicine because of an app interpretation. Recording a value in Today's Vitals is not the same as sending an urgent message to your doctor.

Severe trouble breathing, chest pain, or another medical emergency needs immediate help, even if the display looks normal. Call 911 in the United States. Do not keep repeating measurements while waiting for a number that confirms serious symptoms.

Questions for your next visit

• Is this device appropriate for me, and can we review how I use it?
• What symptoms or changes should prompt a call or emergency help?
• How would you like me to record and share the results?