What can fool the oxygen finger clip?

Understand

A pulse oximeter (the oxygen clip on your finger) estimates oxygen saturation by shining light through your fingertip. Five things that can make the reading less accurate: cold fingers (less blood flow), nail polish or false nails, moving or shivering, a clip that fits poorly and lets room light in, and darker skin: the clip reads light through the skin, skin pigment affects that light, and devices were often tested mostly on lighter skin, so some can read higher than the true level and low oxygen can be missed (TGA safety update; regulators have proposed that makers test across the full range of skin tones). That is why nurses fix what they can, watch the trend, and look at the person, not just the number. The drawings are simplified teaching schematics and the numbers shown are examples.

1. The clip (a pulse oximeter) shines light through the fingertip to estimate oxygen saturation (sats).
2. It needs a good pulse signal and only its own light: cold, movement and room light disturb it.
3. Nail polish, false nails and skin pigment also affect the light.
4. Clips were often tested mostly on lighter skin, so in darker skin they can read higher than the true level.

Key takeaways

• Five things can fool the clip: cold fingers, nail polish or false nails, moving or shivering, a loose clip, and darker skin.
• Fix what you can, then recheck.
• Watch the trend and look at the whole person, not just one number.
• In darker skin the clip can read higher than the true level, so low oxygen can be missed.

In practice

• Fix what you can: warm the hand, keep it still, check the fit; nail polish or false nails: follow local policy.
• Recheck, then watch the trend.
• Look at the person, not just the number. Don't match? Recheck and report.

Check yourself

Mrs Lee is shivering, and her sats reading jumps between 88% and 95%. What first?

Words to know

Pulse oximeter

the clip that estimates oxygen saturation with light (oxi- (oxygen) + -meter (measure))

Sats (SpO₂)

oxygen saturation: how much of the blood's haemoglobin is carrying oxygen

Hypoxaemia

low oxygen in the blood (hypo- (low) + ox- (oxygen) + -aemia (blood))

Transcript

Sources

1. TGA - Limitations of pulse oximeters and the effect of skin pigmentation (Medical Devices Safety Update, 7 Jan 2022): fit, peripheral blood flow, nail coatings, tattoos and dyes; may over-estimate saturation in darker skin so hypoxia could go unrecognised; long/artificial nails and nail polish; use trends and the whole clinical picture (read 10 October 2026)
2. MHRA - The use and regulation of pulse oximeters: information for healthcare professionals (too loose lets light in; motion artefacts; nail polish and false nails; poor circulation incl. cold makes a signal hard to pick up; darker skin may overestimate SpO2; ambient light) (read 10 October 2026)
3. MJA - COVID-19 highlights the need for action on pulse oximeter accuracy in people with dark skin (2022 letter): SpO2 >92% hid ABG <88% nearly 3x more often in black patients; FDA required only 15% of study subjects with darker skin, Australia no requirement; mechanisms still need research (read 10 October 2026)
4. FDA - Draft guidance to improve pulse oximeter performance across skin tones (Jan 2025): more participants, Monk Skin Tone Scale, testing across the range of skin pigmentation (read 10 October 2026)
5. UK Department of Health and Social Care - Equity in medical devices: independent review, summary report (11 Mar 2024): pulse oximeters pass light through the skin and the light reacts differently with varying levels of melanin; testing on participants with light skin tones compounded the bias; they overestimate true oxygen levels in people with darker skin, more so at low saturation; risk of delay in identifying dangerously low oxygen (read 11 October 2026)

Checked against these sources at the time of publishing. Sources change, so check the date above and your local policy. Spotted an error? Tell us and we'll correct it.