Pulse oximeter swayed by skin colour

Published on November 18, 2022 by


Pulse oximeters are widely used by patients at home to check their oxygen levels. 

Bengaluru, November 8, 2022:  In India the issue of inaccurate results in the use of pulse oximeters still go unnoticed. Even many doctors in India do not seem to know about the issue. Recently a research published in the journal, Nature shows people with darker skins are much more likely to get inaccurate oxygen saturation reading by a pulse oximeter. 

Dr Vikash Goyal, a cardiologist based in Bengaluru, said he is not aware of the issue of pulse oximeters showing inaccurate results on darker skin. “I have never encountered any of this problem during my practice.” he said.

The presence of more melanin in people with dark skin affects oximeter signals and thus accounts for overestimation of blood oxygen level. They are said to have occult hypoxemia – a state when an arterial oxygen saturation level is less than 88% while the pulse oximeter oxygen saturation is between 92–96%. 

Pulse Oximeter is the standard in the primary and intensive care unit, especially in the post-covid time. It estimates the level of oxygen by shining red and infrared light through the fingertip. This is thus absorbed by the oxygenated haemoglobin. In a healthy individual, infrared light is absorbed more efficiently than the red light. The exact opposite is true for people with deoxygenated haemoglobin. A recent study published in JAMA Internal Medicine found that the inaccuracies in the oximeter readings can also be associated with the disparities in their care. 

Dr Vinod Kolla, Pulmonologist at Rajarajeshwari Medical College and Hospital, said, pulse oximeters show around 5 percent of difference in results when used on people with darker skin. “The difference is most evident when the oxygen saturation level is less than 85. The presence of melanin acts as a hindrance. For example while using pulse oximeters it is advisable to remove red nail paint, because it affects the accuracy,” he added.

Another study published in the National Centre for Biotechnology Information shows the pulse oximeters’ accuracy in dark skin individuals is less especially at lower oxygen saturation. This means it is harder for darker skinned patients to be diagnosed with hypoxaemia. Studies show discrepancy in results can range from two to eight percent, which can be significant in the cases of hypoxia and jaundice. The issue has not found much ground in India as the awareness among doctors in the country remains very less.

Experts believe many doctors are unaware of the issue as they don’t use pulse oximeters on a daily basis. Dr Deepak Kumar, senior Consultant at Metro Hospital and Cancer Institute, Delhi, said, “As a medical practitioner you need to know about the issue. I think we need to conduct seminars and CMEs (continuing medical education) to educate and spread awareness among doctors.”

Multiple research is going on regarding finding a solution to biasness of pulse oximeters. One of them is the research done by Brown University Ph.D. students from the department of Physics. Recently BioIntelliSense, a medical equipment manufacturer, unveiled a pulse oximeter sensor chipset and processing technology that accurately measures oxygen saturation across different skin tones. In this technology, in addition to traditional lights, a white light emitter combined with a spectral sensor is used. This comes amid the U.S Food and Drug Administration (FDA) held a meeting on November 1 to discuss racial disparity in pulse oximeters. 

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