An early warning monitor designed to watch for falling oxygen levels in Covid-19 patients does not work as well for people with darker skin tones, UK experts said on Saturday.
The National Health Service, the UK state-funded health service, is updating its advice to patients after the shortcoming in the pulse oximeter was realised.
The device, which is used by people at risk of developing severe Covid symptoms, beams light through the blood to detect oxygen levels.
But now NHS England has noted it is less accurate when used on patients with darker skin pigmentation.
Dr Habib Naqvi, director of the NHS Race and Health Observatory, welcomed the new guidance.
“Although a valuable clinical tool, clinicians are increasingly becoming aware of the potential errors or inconsistencies associated with pulse oximeters, so we need to have this in mind when using the devices,” he said.
Patients using the oximeter should look for changes over time and not rely on a single reading, NHS England said.
The device, clipped to a finger, checks blood-oxygen levels and below a certain reading the patient will need to be hospitalised.
The NHS supplies them to people with virus symptoms, aged over 65 or clinically vulnerable.
The NHS said in a statement that “there have been reports that pulse oximeters can be less accurate for people with darker skin because they may show higher readings of the oxygen level in the blood".
Updated guidance for virus sufferers on the main NHS website now warns: “There have been some reports they may be less accurate if you have brown or black skin.
“They may show readings higher than the level of oxygen in your blood.”
But the important thing is to check regularly whether to see if they are going down, it adds.
Members of ethnic minorities, particularly Black Africans and Bangladeshis, have suffered the highest death rates from the virus in Britain, government figures have shown.
The seven-day average of new Covid-19 cases in Britain fell to 28,272 on Friday, a drop of 36 per cent in a week.
But the latest results from an infection survey by the Office of National Statistics showed cases in England continuing to rise.
The ONS survey is seen as reliable because it randomly samples the population, but it typically lags behind the government’s daily numbers.
“Overall, we are seeing chaotic data sets that reflect a lot of different things happening at the same time,” said Dr Simon Clarke, a microbiologist at the University of Reading.