Have you had COVID-19? Evaluating the effectiveness of antibody tests

Christiane Barro
Sep 25, 2020, updated Sep 25, 2020

The best time to see if you’ve developed antibodies against the coronavirus is at least 20 days from when you first start having symptoms.

That was the conclusion researchers from King’s College London drew after an experimental study of 10 commercial antibody test kits, which look at a person’s blood to detect whether they had COVID-19.

How the 10 test kits performed varied widely. They ranged from 82 to 100 per cent in their ability to identify who was no longer infectious, and 60.9 to 87.3 per cent when it came to seeing who still had the virus.

Researchers also found antibody levels were higher in people who had a severe form of the coronavirus as compared to those who were asymptomatic or had a mild form of the disease.

The performance of the test kits was highly dependent on the time a blood sample was taken from a coronavirus patient.

All achieved the best results when used 20 days or more after the start of symptoms, during which time most tests reached a sensitivity value greater than 95 per cent.

The tests that were able to pinpoint who recovered from the virus with at least 98 per cent accuracy were called Accu-Tell, SureScreen and Spring.

“We found that some of the quick single-use kits (LFIAs) are as accurate as our sophisticated laboratory technologies,” co-author of the study Jonathan Edgeworth said.

“Encouraged by these findings we are piloting LFIAs in the hospital to give doctors a quick reliable answer in a range of clinical settings.”

The blood is thought to contain antibodies which can help fight COVID-19. Photo: Red Cross Lifeblood

At least 14 different antibody tests have been approved by the Therapeutic Goods Administration for legal supply in Australia, giving medical professionals the ability to monitor the coronavirus in patients.

The TGA prohibits the supply of self-tests for COVID-19 and last week noted on its website that it was not yet evident whether the presence of antibodies meant someone was immune to the virus.

And the detection of antibodies may not mean an infected person has recovered from the virus, it said on its website.

There is also the question of how long do the antibodies last.

England’s chief medical officer, Professor Chris Witty, this week revealed in a press conference that there were indications the antibodies can “fade” in some people who have recovered from the coronavirus.

However, the UK National Health Service said antibody tests are to “help the NHS and scientists learn more about who has already had the virus and how it has spread in the UK”.