Coronavirus antibody home tests not sensitive enough, study suggests

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

But researchers said a laboratory test – 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.

The authors write that 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.

However, the early promise of lateral flow immunoassay (LFIA) devices – the fingerprick-type home tests – has been questioned following concerns about sensitivity and specificity.

Professor Derrick Crook, of the Nuffield Department of Medicine and NIHR Oxford Biomedical Research Centre, University of Oxford, is the corresponding author of the study that has not been peer-reviewed.

The authors conclude: “The performance of current LFIA devices is inadequate for most individual patient applications.

“ELISA can be calibrated to be specific for detecting and quantifying SARSCoV-2 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, is also detected by the coronavirus tests.

It shows that someone has had the virus and is now protected from it.

This can be detected in a patient’s blood 10-14 days after infection.

In their pre-print study, the researchers tested 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 estimates the sensitivity of LFIA devices ranged from 55-70% versus RT-PCR test which diagnoses Covid-19, and 65-85% versus ELISA, with specificity 95-100% and 93-100% respectively.

Commenting on the findings, Richard Tedder, visiting professor in medical virology at Imperial College London, said: “The Oxford group study compares the performance of nine unnamed point-of-care tests (PoCT) against an in-house conventional indirect immunoassay (ELISA) for IgG and IgM antibody using a tri spike antigen.

“This ELISA has a claimed 85% sensitivity in detecting antibody in known cases. It also has a claimed 100% specificity on a small panel of 50 pre-Covid 19 samples.

“In comparison, the PoCT sensitivities ranged for 70% down to 55%.

“The PoCT specificities ranged from 100% down to 95%.

“However, the samples used for this latter determination appear to be different and of larger numbers than those used for the in-house ELISA determination, making objective comparisons of specificity somewhat difficult and at best inexact.

“Interesting though the data are, they are simply of no value at this time as there is no way of relating the Oxford findings of an in-house assay to those PoCT assays which are currently known about in this country.”

Eleanor Riley, professor of immunology and infectious disease at the University of Edinburgh, 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.”

The authors summarise: “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.”