OXFORD researchers have found coronavirus antibody tests might not give a positive result if people have only had mild symptoms, like loss of taste and smell.

Microbiology and data experts from the Oxford University Hospitals NHS Foundation Trust (OUH), which runs the John Radcliffe, and Oxford University made the initial findings, as part of a comprehensive testing programme for OUH staff.

The researchers previously found that among trust staff an isolated loss of smell or taste was strongly predictive of Covid-19 infection, as defined by a positive swab or antibody result.

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Antibody results are however defined by a threshold set against a continuous scale with only readouts above the threshold defined as ‘positive’.

Dr Tim Walker, one of the authors of the paper, said: “Our dilemma is that some people with a mild form of the disease can fall into an ‘equivocal’ zone that is currently classed as ‘negative’ result.

"Lowering the threshold to reclassify some false negatives as ‘positives’ will inevitably mean that some true negatives will then wrongly be categorised as positive.

“When we adjust for the likely proportion of staff reporting a loss of taste or smell due to reasons other than Covid-19, it suggests that the sensitivity of the antibody tests are nine to 11 per cent lower than had previously been reported."