Accuracy and value of antibody tests dismissed after global review

‘They have an important role in understanding and mapping the disease, but are individually questionable’

Sarah Knapton

ANTIBODY tests could do more harm than good by giving people false hope that they are protected from Covid-19, scientists have warned.

A global team of researchers led by British experts carried out the most comprehensive review to date into tests’ reliability.

They found that tests must be done at least two weeks after symptoms develop, as those carried out within one week picked up fewer than 30 per cent of people who had been infected, and under two weeks around 70 per cent.

After two weeks, the chance of picking up antibodies rose to around 90 per cent, but 10 per cent of infected people still received a false negative, making it seem they did not have the virus.

On the value of antibody testing, Jon Deeks, professor of biostatistics and head of the Test Evaluation Research Group at the University of Birmingham, said: “It’s giving people the sense that they may be immune. There is no decision they should be making based on the results of this test. The tests have an important public health role in understanding and mapping disease, but individually are questionable.”

The Government had hoped antibody testing could identify people immune to the virus who could go about their lives without risk of infection. But studies have now shown that not everyone infected will develop antibodies, particularly those with mild doses.

Likewise, false positives may encourage people to be less scrupulous with social distancing and hygiene.

The review authors also warned that they had “no idea” if the tests were accurate beyond 35 days of symptoms emerging as no studies had been carried out for that length of time. It is also

unclear whether tests can detect lower antibody levels associated with milder and asymptomatic Covid cases, as testing so far has been carried out in hospital patients with severe illness.

The team reviewed more than 11,000 publications on Covid-19 available at the end of April, and identified 54 relevant studies from Asia, Europe, and the US, assessing antibody test accuracy.

All tests were poor at detecting disease during the first week after symptoms, and rose steadily as more immunity built in the body.

“These tests may help identify Covid-19 in people who have had symptoms for two or more weeks but never had a swab test, and identifying how many have had infection to assess disease spread,” added Prof Deeks.

“In time, we will learn whether having previously had the infection provides individuals with immunity to future infection, which will indicate the personal value of having this test.” The report was published in the Cochrane Database of Systematic Reviews.