Coronavirus antibody home tests not reliable, study finds

Rapid coronavirus antibody home tests cannot currently be relied on to provide accurate results, according to a new study.

But British researchers said a laboratory process, known as Elisa, showed promising results when indicating whether someone had developed Covid-19 antibodies.

The investigations were led by the National Covid Testing Scientific Advisory Panel.

Researchers noted in their study there is an urgent need for robust antibody detection approaches to support diagnostics, vaccine development, safe individual release from quarantine and population lockdown exit strategies.

But the early promise of fingerprick-type home tests known as lateral flow immunoassay (LFIA) devices — millions of which have been purchased by the UK government — has been questioned following concerns about sensitivity and specificity.

Professor Derrick Crook, an infectious diseases expert at the University of Oxford, is the corresponding author of the study, which has not been peer-reviewed.

The researchers said their findings showed the performance of LFIA tests was “inadequate for most individual patient applications”.

But they said Elisa “can be calibrated to be specific for detecting and quantifying [coronavirus antibodies] IgM and IgG and is highly sensitive for IgG from 10 days following symptoms onset”.

The antibody IgM is the body’s first response to an infection — normally within five to 10 days of an infection taking hold, peaking at 21 days after the infection.

The other antibody, IgG, shows that someone has had the virus and is now protected from it. This can be detected in a patient’s blood 10 to 14 days after infection.

In their pre-print study, the researchers used the tests on samples from 40 people.

The Elisa test detected both Covid-19 antibodies in 34 of the 40 patients, with the diagnosis confirmed with a separate test.

IgG levels were detected in 31 out of 31 patients tested 10 or more days after symptom onset.

The research tested nine unnamed LFIA devices, and used their sensitivity to range from 55 to 75 per cent versus the RT-PCR test, which diagnoses Covid-19. They ranged from an estimated 65 to 85 per cent versus Elisa.

The authors summarised: “Antibody testing is crucial to inform release from lockdown.

“This study offers insights into the performance of both a novel Elisa and a panel of LFIA devices that have been made widely available, but to date with limited systematic validation.

“Our findings suggest that while current LFIA devices may provide some information for population-level surveys, their performance is inadequate for most individual patient applications.”

Eleanor Riley, a professor of immunology and infectious disease at the University of Edinburgh who was not involved in the study, said: “This is a really useful paper.

“It shows that the problem with the commercial rapid antibody tests is that they are not sensitive enough — they fail to pick up antibodies in over a third of people who do in fact have antibodies.

“However, these tests do have acceptable levels of specificity, that is, they are only picking up people who have genuinely been exposed to the Covid-19 virus.

“This means if your test is positive, you can be confident that you have been infected and have antibodies. But if your test is negative, you can’t rule out that you might have been infected.

“Just as importantly, this paper shows that we do have a very good assay for use in the lab.”

Richard Tedder, visiting professor in medical virology at Imperial College London, said the study was “interesting” but “simply of no value at this time as there is no way of relating the Oxford findings of an in-house assay to those point-of-care test assays which are currently known about in this country”.

The UK government’s testing chief has previously admitted none of the 3.5 million antibody tests ordered by the government were fit for widespread use.

Professor John Newton, who was appointed by health secretary Matt Hancock to oversee testing, said the tests were only able to identify immunity in people who had been severely sick with coronavirus and were “not good enough to be worth rolling out in very large scale”.