A device designed to spot early signs of dangerous falls in oxygen levels in Covid patients works less well in those with darker skin, experts are warning.
NHS England is issuing updated guidance, advising patients from black, Asian and other ethnic minority groups to continue using pulse oximeters, but to seek advice from a healthcare professional.
An NHS Health and Race Observatory report published in March recommended that the MHRA should carry out an urgent review into the use of pulse oximeters.
In people with Covid-19, oxygen levels in the blood can drop to dangerously low levels without them noticing - a condition known as "silent hypoxia".
Ranjit Senghera Marwaha bought a pulse oximeter while unwell with coronavirus last year, but her oxygen levels dropped so low that she had to be hospitalised.
"When I went into hospital the first thing they said was, 'you've really left it too late,'" Ms Marwaha said.