What you need to know about COVID-19 antibody tests

A COVID-19 antibody test is now generally available to Kingston residents, with a doctor’s requisition. The medical laboratory chain Life Labs began offering the Health Canada approved serology test on Monday, Nov. 23, 2020. Currently available in British Columbia and Ontario, the test costs $75.

However, internal medical expert Dr. Gerald Evans advises that the results of a COVID-19 antibody tests are not always straightforward. He said he can’t think of many clinical circumstances when a doctor would request this information.

“Really it has very little utility in the general practice of medicine,” he said. “Right now the only use that we have for an antibody test, based on the guidelines that are issued, is to use it to investigate children who present with a multi inflammatory syndrome (IMSC)…. That’s really the only clinical utility we have for it,” he said.

He also explained that not everybody who gets COVID-19 exhibits the exact same antibody response, which makes the virus different from others such as measles or chickenpox.

“Most people get something, but some people are what we call ‘low-level responders,’ meaning the levels of antibodies that they get could be below a detection level that we’re looking for.”

“So if you wanted to do this test because you’re saying ‘I recall being ill and I think it was COVID,’ you do an antibody test. If it’s negative, it doesn’t really say that you didn’t have a COVID-19 infection. It may mean that you were one of these people that had a very mild infection and didn’t get a big antibody response.”

He also explained that humans make three different types of antibodies in response to a virus — IgG, IgA, IgM.

“IgM antibodies disappear very quickly. If you’re more than a couple of months out from your infection, you won’t find them. IgA antibodies are super tricky because they go up and down, they disappear, and some people don’t make them at all.”

The IgG antibody, which he said believes the Life Labs antibody tests are based on, is much more stable.

Life Labs CEO Charles Brown called antibody testing “another piece of the puzzle to better understand COVID-19.”

The company also explains on their website that a negative result might mean a person has been infected, but that antibody levels were too low for the test to detect. They note that you might receive a negative result, even after being infected, if not enough time has lapsed since the infection, to allow for antibodies to develop.

“Antibody response varies from person-to-person and can take up to three to four weeks post-onset of symptoms or post-exposure to be reliably detectable by antibody assays,” the company said.

Both Dr. Evans and Life Labs note that the test cannot be used to determine a current infection.

“It doesn’t really help in the diagnosis of COVID-19. Antibodies are made after you’re infected or when you’re in that recovery phase,” Dr. Evans said.

COVID-19 antibodies do not mean immunity

Dr. Evans said that typically, the IgG antibodies for the measles can be detected by a test in anyone that has ever had, or been inoculated against, the virus, even years later. They also indicate immunity. In the case of COVID-19, he said, it’s not the same thing.

“We still don’t quite have the exact test that tells us that those antibodies we’re measuring are at a high enough level or are responsible for neutralizing the virus, which would then predict that you’re immune,” he said.

“We’ve found people that even have these antibodies, they may not be in sufficient quantity. Or, it may not be the right antibody that actually protects them and gives them immunity. That’s the big problem.

“You could imagine somebody saying: ‘I’m going to get the test done to show that I’m immune,’ and that’s not really what it’s telling you.”

Life Labs website states that a positive test result does not infer immunity. They recommend getting the blood test three to four weeks after the onset of symptoms, adding that it’s possible to detect antibodies up to four months post-exposure.

“We look forward, to continue building our support for the healthcare system’s response to the pandemic, where Canadians have access to more important COVID-19 information to help them make informed decisions about their health,” Brown said.