Coronavirus Antibody Tests – Are They Accurate?

US researchers are testing over 100 coronavirus antibody detection products, but even they can’t agree on the significance of the results

American researchers have been testing the accuracy of coronavirus antibody detection kits, but even they can’t agree on what the results mean.

Health services all over the world are putting faith in antibody detection kits to help get a handle on the coronavirus pandemic. The idea is that if a subject has been exposed to coronavirus, their immune system will have produced antibodies of different types. According to the levels of different types of antibody in the system, the tests should be able to determine whether the subject is free of infection, is currently infected, or has recovered from infection.

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The question is whether the 100 or more makes of antibody testing kit available on the open market are reliable. A team of over 50 American scientists started off by testing the accuracy of 14 different kits, and the results made interesting reading.

Consistently reliable

Of the 14 tests, only three delivered consistently reliable results, and even the best had some flaws. One, manufactured by Sure Biotech in China, showed promising results with 100 percent specificity – but even the manufacturer itself does not claim that its test is that accurate.

The problem is that it isn’t safe to assume that a subject is fit to return to work, if the test isn’t 100 percent accurate.

The researchers procured hundreds of blood samples from two Bay Area hospitals, and purchased tests from Chinese manufacturers. They analysed 10 rapid tests that deliver a yes-no signal for antibodies, and two tests using a lab technique known as Elisa that indicate the amount of antibodies present and are generally considered to be more reliable.

The New York Times reported: “Researchers found that only one of the tests never delivered a so-called false positive — that is, it never mistakenly signalled antibodies in people who did not have them.

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“Two other tests did not deliver false-positive results 99 percent of the time.

“But the converse was not true. Even these three tests detected antibodies in infected people only 90 percent of the time, at best.

“The false-positive metric is particularly important. The result may lead people to believe themselves immune to the virus when they are not, and to put themselves in danger by abandoning social distancing and other protective measures.”

Just how accurate

So the question is – how accurate does an antibody test need to be?

Dr. Alexander Marson, an immunologist at the University of California, San Francisco, and one of the project’s leaders, said “There are multiple tests that look reasonable and promising – that’s some reason for optimism”, but Scott Hensley, a microbiologist at the University of Pennsylvania, said “Those numbers are just unacceptable. The tone of the paper is, ‘Look how good the tests are.’ But I look at these data, and I don’t really see that.

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“If your kit has a 3 percent false-positive, how do you interpret that? It’s basically impossible,” he said. “If your kit has 14 percent false positive, it’s useless.”

The research has not been peer-reviewed and is subject to revision. But the results are already raising difficult questions about the course of the epidemic, and at what point testing will be reliable enough to dictate a course of action for the health authorities and governments of the world.

In the UK, Health Secretary Matt Hancock said on April 3rd that the British government had not yet found an antibody test that is “good enough to use.”

“I get pressure on this. I get people saying ‘oh come on, it may not be perfectly accurate but can’t we just use it,” he stated.

“The problem is that with a test that is not of high quality, you end up giving false assurance.”

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