Which factor is NOT listed as affecting SpO2 readings?

• A. Dark nail polish
• B. Cold extremities
• C. Tremors
• D. Bright light

Answer: (D)

Pulse oximetry relies on photoplethysmography: a sensor shines light into tissue and detects how much is absorbed by oxygenated versus deoxygenated hemoglobin as blood pulses. Anything that disrupts the light path or the pulsatile signal can skew the reading.

Dark nail polish sits on the nail bed and can absorb or scatter light in a way that the sensor interprets as a lower oxygen saturation, or it can cause erratic readings. Cold extremities reduce blood flow to the fingertips through vasoconstriction, weakening the pulsatile signal the sensor depends on and making readings less reliable. Tremors introduce motion artifacts, changing the optical path as the hand moves and distorting the waveform the device uses to calculate SpO2.

Bright ambient light, however, is not typically listed as a factor that affects SpO2 readings. Modern sensors are designed to filter background light and rely on the pulsatile signal, so ambient brightness usually doesn’t compromise the measurement unless the device is poorly shielded or defective.