Pulse oximeters may be overestimating oxygen saturation in dark skin-toned people, study finds

New Delhi: Pulse oximeters, now common in many households for measuring oxygen saturation in blood, could be overestimating their readings in dark-skin-toned people, new research analysing 44 studies over the last five decades has found.

Researchers in the UK assessed more than 733,000 oxygen saturation readings taken from over 222,000 people, including almost 70,000 people of non-white ethnicity.

The team said that most of the studies (30 out of 44) analysed revealed evidence of these medical devices being inclined to overestimate oxygen saturation in blood in participants with darker skin tones, even though they found it challenging to determine "by how much", based on the currently available data.

The researchers said that a major finding in these studies related to the incidence of occult hypoxaemia - medical condition of having abnormally little oxygen in the blood - with an incidence of up to 21.5 per cent in Black patients.

"Most studies reported an occult hypoxaemia incidence 25-75 per cent higher in Black compared with White patients, with other ethnic groups having a 25-50 per cent higher incidence," the researchers wrote in the study published in the British Journal of Anaesthesia.

They did insist, however, that the overestimation could create issues for both patients and medical professionals in that patients with actual critical oxygen levels not receiving the treatments that they direly need.

The overestimation could also prevent patients from seeing a doctor, as it might deem them "healthy", the team said.

"As clinicians, we rely on accurate data to make informed clinical decisions. But during the Covid pandemic, and to some extent since it was necessary to put thresholds in place which meant that people were only admitted to hospital if their levels fell to a certain point," said lead author Daniel Martin, Professor of Perioperative and Intensive Care Medicine in the University of Plymouth, UK.

"If those levels are being overestimated - so, for example, if a device is telling someone their oxygen saturation is 98 per cent whereas it is in fact significantly lower - it could realistically mean people are missing out on treatments they need," said Martin.

He said that the concern arose out of the use of these devices in the community, where additional tests to ascertain unwell patients like blood tests and physical assessments are not available as they are in hospitals and other healthcare settings.

Acknowledging limitations to the study, the researchers said all the studies were conducted in high-income countries, where the majority of the population have light skin tones.

This they said was relevant as low- and middle-income countries often have a higher proportion of people with darker skin tones and funding for healthcare may be such that pulse oximetry is the only available monitor for unwell patients.

The study findings are currently being explored in more detail, the researchers said, with recruitment of 900 critically ill patients differing in skin tones underway in the UK.