If you have been sick at all since December 2019, even with a slight sniffle, you have probably wondered if whatever you had was actually the novel coronavirus. You might have discussed getting an antibody test, and while the development of antibody tests is an extremely important element in containing the coronavirus pandemic, it turns out the accuracy of the tests rely on one crucial factor.
An antibody test picks up on immune proteins in the body, which can help determine who has COVID-19. On the other hand, a polymerise chain reaction (PCR) test is able to detect if a person is currently infected with the virus.
A new large review of studies has shown that timing is crucial when it comes to the antibody test.
When are antibody tests most accurate?
The Cochrane review of studies found that the accuracy of an antibody test is far lower if it is used within the first two weeks of coronavirus symptoms, rather than a week or two later.
A team of researchers examined 54 studies of antibody tests that were carried out on about 16,000 samples, more than half of which were from coronavirus cases. The review suggests that the studies were often problematic as many failed to give clear details about the actual number of patients that were involved or the actual test used.
“People who are hospitalised with COVID-19 infection have severe infection and they probably have high levels of antibodies as a result of this,” said Jon Deeks, a member of the Cochrane review and a professor of biostatistics at the University of Birmingham. “This is going to lead to tests looking more sensitive than they would be if we used them in the general population.”
The review uncovered that the timing of an antibody test is absolutely crucial to the accuracy of the test.
“What our analysis has most clearly shown is that this [variations in the accuracy of tests from different studies] is largely driven by when the samples are taken from the patients,” said Deeks.
Is it bad to wait too long to do an antibody test?
“We don’t really know very much about the accuracy of these antibody tests after the first five weeks of the disease,” said Deeks.
According to Deeks, antibody testing could be beneficial in testing people with symptoms of COVID-19 and also in determining the levels of infection in large populations if the tests are able to puck up antibodies a few months after infection occurs, but antibody tests do not offer any information about immunity to the virus in an individual.
Other immunologists agree that timing is crucial when it comes to the accuracy of antibody tests.
“It is already very clear from this analysis that antibody testing early in the course of disease is unreliable and thus antibody tests cannot, and should not, replace virus detection for diagnosis of acute cases except where the time-course of disease is already well advanced,” Eleanor Riley, a professor of immunology and infectious disease at the University of Edinburgh and who was not part of the review team, told The Guardian.
If you think you had COVID-19, should you try to get the antibody test?
According to Riley, the data makes it clear that most commercially available tests are not accurate enough to warrant their use outside of the healthcare setting.
The use of the antibody tests in hospitals could improve the understanding of how coronavirus spreads in healthcare settings and provide more information about appropriate actions to take, but the tests offer very limited benefits for an individual who thinks they might have had COVID-19.
“Doing this in a coordinated way, with public health input, would be the critical way to make the most [of] this testing,” Deeks said.
Jennifer Fabiano is an SEO reporter at Ladders.