SpO2 on a pulse oximeter (oxygen saturation, %SpO2)
SpO2 is the oximeter’s estimate of oxygen saturation: how much of the haemoglobin in the blood at your fingertip is carrying oxygen, as a percentage. The oximeter works it out from how red and infrared light pass through the finger with each pulse, so it is an estimate from light, not a blood test.
Check your oximeter’s manual — makers differ.
What it is for
Read it only once the signal is steady. Nonin says to “observe about 4 seconds of continuous green-colored pulse quality before relying on the displayed values” on the Onyx Vantage 9590, and Microlife says the OXY 300’s bar “should be greater than 30 % for a proper reading”. On what the number means for health, the makers cited say different things. Beurer is the only one that prints a table: its PO 30 and PO 45 manuals class 99–94 as “Normal range”, 93–90 as “Decreased range: visit to the doctor recommended” and below 90 as “Critical range: Seek medical attention urgently”. Beurer warns in the same place that its table “does NOT apply to people with certain pre-existing conditions (e.g. asthma, heart failure, respiratory diseases) or whilst staying at altitudes above 1500 metres”, and its PO 45 manual gives the table’s source as Windisch W et al., a 2017 guideline on home mechanical ventilation published in Pneumologie. Masimo’s MightySat manual gives no table and says: “Always consult your physician regarding clinical decisions.”
These pages report what each maker’s manual says and quote it wherever health is involved. They do not diagnose anything, they are not medical advice, and they do not tell you whether an oxygen or pulse reading is right for you or what to do about it; only your own oximeter’s manual and your doctor or nurse can do that for the person you are looking after.
- What it looks like
- One of the two main numbers, marked %SpO2 or SpO2 beside it or in the display key.
- Names makers use
- %SpO2 (Nonin Onyx Vantage 9590, Beurer PO 30, PO 45 and PO 60, Microlife OXY 300); SpO2 (Masimo MightySat Rx); Oxygen saturation (value in percent) (Beurer and Microlife display keys)
Where makes differ
Accuracy is quoted per maker, as Arms, a root-mean-square error against blood samples. Nonin’s 9590 leaflet gives ±2 digits over 70 to 100% on fingers, Masimo’s MightySat manual 2% at rest and 3% in motion over 70 to 100%, Beurer’s PO 60 and PO 45 manuals ±2% over 70 to 100%, and Microlife’s OXY 200 manual “≤3% (70% – 100%)”. Microlife’s OXY 200 manual also explains what Arms means: “only about two-thirds of pulse oximeter equipment measurements can be expected to fall within ±2% A rmse” of a laboratory co-oximeter. The Microlife OXY 200 beeps as a “risk reminder” when SpO2 is “lower than 94%”, while the Nonin, Beurer and Microlife OXY 300 manuals say those models have no alarm. Beurer (PO 45) says that if the measured SpO2 is too low, below 70%, to measure again and, if it keeps happening and the device is working, to “seek medical advice as a matter of urgency”.
What it does not mean
It is not the amount of oxygen you breathe or the oxygen level in the air. It is not reliable in every case: Beurer’s manuals say carbon monoxide poisoning makes the reading too high, and Nonin lists anaemia, nail polish, artificial nails, bright light and movement among the things that degrade it.
Other symbols with the same shapes
Sources
No published standard we could check defines what a fingertip pulse oximeter’s display shows, so this meaning is taken from 4 makers’ own manuals and support pages, each fetched and read on the date shown:
- Nonin: Nonin Onyx Vantage 9590 finger pulse oximeter — instructions for use (P/N 10906-001-04, 2020, PDF) — Activating the 9590: numeric LEDs display oxygen saturation and pulse rate; “observe about 4 seconds of continuous green-colored pulse quality before relying on the displayed values”; declared accuracy 70 to 100% ±2 digits (Arms); factors that degrade performance. Checked 2026-09-29.
- Masimo: Masimo MightySat Rx fingertip pulse oximeter — operator’s manual (LAB-9121C, PDF) — Functional Oxygen Saturation (SpO2): “the amount of oxyhemoglobin expressed as a percentage of the hemoglobin that is available to transport oxygen”; SpO2 accuracy 2% (no motion) and 3% (motion) Arms, 70% to 100%. Checked 2026-09-29.
- Masimo: Masimo MightySat Rx fingertip pulse oximeter — home care manual (PDF) — General warnings: “Always consult your physician regarding clinical decisions.”; display range SpO2 0% to 100%. Checked 2026-09-29.
- Beurer: Beurer PO 30 pulse oximeter — instructions for use (2020-01-08, German/English, PDF) — Display description: 1. Oxygen saturation (value in percent); section 9, Evaluating measurement results: the SpO2 table (99-94 Normal range, 93-90 Decreased range, < 90 Critical range) and its warning for pre-existing conditions and altitudes above 1500 m. Checked 2026-09-29.
- Beurer: Beurer PO 45 pulse oximeter — instructions for use (2020-06-12, German/English, PDF linked from beurer.com) — Section 9: the same SpO2 table, sourced to Windisch W et al., Pneumologie 2017; troubleshooting: measured SpO2 too low (< 70 %), “seek medical advice as a matter of urgency” if repeated; accuracy 70–100 %, ± 2 %. Checked 2026-09-29.
- Microlife: Microlife OXY 300 fingertip pulse oximeter — instruction manual (IB OXY 300 N-V9, revision 2023-11-30, PDF) — Explanation of symbols: 2 Oxygen saturation (value as percentage); the bar graph “should be greater than 30 % for a proper reading”. Checked 2026-09-29.
- Microlife: Microlife OXY 200 fingertip pulse oximeter — instruction manual (IB OXY 200 S-V10, 2026-09-14, PDF) — Risk reminder: a warning sound if SpO2 is lower than 94%; measurement precision ≤3% (70% – 100%); note on Arms (about two-thirds of readings within ±2%). Checked 2026-09-29.
Written in our own words; quotations are the makers’ wording.