Impact of Skin Pigmentation on Pulse Oximeter Accuracy

Pulse oximeters are essential tools in medical settings, widely used to monitor blood oxygen saturation levels noninvasively. They work by emitting red and infrared light through the skin and analyzing how much light is absorbed, providing quick estimates of oxygen levels in the blood. However, recent research has raised concerns about the reliability of these devices across different skin tones.

Clinical studies have highlighted that pulse oximeters tend to overestimate oxygen levels in individuals with darker skin, especially when oxygen levels are low, a condition known as hypoxemia. Such inaccuracies can delay diagnosis and lead to less effective treatment, raising questions about device calibration and bias.

To investigate this issue, a study led by researchers from the University of North Carolina and Washington University employed a novel animal model—Hampshire pigs with naturally dark and light skin patches. This approach allowed for direct comparison of pulse oximeter readings from pigmented versus non-pigmented areas on the same animal under uniform conditions.

The researchers developed custom pulse oximeters and gradually decreased the pigs' oxygen levels from 100% to about 70% while collecting arterial blood samples for precise oxygen saturation measurements. They analyzed how red and infrared light absorption changed over time, leveraging advanced signal processing to distinguish pulsatile signals associated with heartbeat.

Findings revealed that in pigmented skin, red light was more heavily attenuated before reaching the blood vessels, impairing the device’s ability to accurately detect oxygen level changes. This effect was especially pronounced during low-oxygen conditions, which are the most critical for accurate assessment.

The results confirm that skin pigmentation influences the physics of light absorption in pulse oximetry, primarily affecting the red wavelength. These insights underpin previous clinical observations of bias and suggest that the interaction of light with pigmented tissue is a key factor.

The study emphasizes the need for further research in humans and calls for designs that consider skin tone variations to improve accuracy. Addressing this bias is vital to ensure equitable and reliable blood oxygen monitoring for all patients, regardless of skin color.

Source: https://medicalxpress.com/news/2025-07-skin-pigmentation-pulse-oximeter-accuracy.html