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What Is COVID-19 Antibody Testing And How Does It Work?

They’re also known as serology tests. But how effective are they?

Maybe you had COVID-19 and didn’t even know it.

It’s a thought on many Canadians’ minds as we enter another month of the coronavirus pandemic. While the total number of test-positive cases in Canada has surpassed 100,000, the number of people who have actually been infected with the virus is likely much much higher. That’s because many people show few or no symptoms, didn’t get tested or were infected before we understood the scope and scale of the virus.

One way to better understand the full spread of COVID-19 is through widespread serology testing to see who has the disease’s specific antibodies — indicating they were infected before and possibly better primed to fight it again.

Blood can be tested for coronavirus antibodies.
busracavus via Getty Images
Blood can be tested for coronavirus antibodies.

Canada is ramping up widespread antibody testing through Canadian Blood Services to help better understand the spread of COVID-19. Officials expect to test tens of thousands of blood samples in the coming weeks to understand better who has these antibodies.

But what is serology testing and how does it help fight COVID-19? And how effective is it in our efforts to fight COVID-19?

Here’s what you need to know.

What is a coronavirus antibody test?

An antibody test, also known as a serology test, looks for specific antibodies in your blood that could indicate a past COVID-19 infection.

Antibodies are disease-specific proteins that help fight off infections and can provide protection against getting that disease again. Antibodies are primed and ready to go to reproduce and fight the virus. So the presence of COVID-19 antibodies could show that you’ve had the disease already.

Wait, does that mean I’m immune if I test positive for the antibodies?

Not necessarily. Because the novel coronavirus that causes COVID-19 is so new, research is still being done on whether or not antibodies indicate immunity, or how long any protection might last. So that idea of “immunity passports” — documents showing you’ve already contracted the virus to allow you to operate more freely in society — is actually a long way off at the moment.

And antibody tests aren’t always accurate. In some circumstances, a positive test result could mean you have antibodies from a different coronavirus infection such as the one that causes the common cold. And a negative test doesn’t necessarily mean you were never infected. It can mean that the body’s immune system response was not strong enough to make enough antibodies, or that there has not been enough time for antibodies to develop.

In the U.S., the Centers for Disease Control and Prevention have warned that these tests can deliver false results up to 50 per cent of the time.

And new research out of McGill University casts doubts on the effectiveness of antibody tests. The research, which involved a review of all known studies on antibody testing effectiveness, found particular weakness in the types of tests that aren’t processed in labs, called lateral flow immunoassay (LFIA) tests.

These are the types of antibody tests being pushed for use in the U.S., largely due to their low cost and fast turnaround times. But the researchers found a large prevalence of false negatives in sample sizes from these types of tests.

“Overall, the poor performance of existing serological tests for COVID-19 raises questions about the utility of using such methods for medical decision making,” they wrote.

Can an antibody test show if I have COVID-19?

In most cases, no. According to the Centers for Disease Control, it takes your body one to three weeks after you were first infected to make the antibodies, so they likely wouldn’t show up if you’re early on in your COVID-19 infection. Testing to see if you currently have COVID-19 involves identifying the virus in your respiratory system.

Why are antibody tests important?

When administered properly and accurately, widespread antibody testing can give officials and researchers a better idea of how many people actually have been infected with the virus. Antibody testing can show if you had COVID-19, even if you had incredibly mild or no symptoms.

In the U.S., the CDC studied antibody testing results in five states, including New York, which indicated an infection rate of nearly seven per cent — a sharp contrast to the around two per cent of people that have tested positive for COVID-19 in the state. That indicates that many people have been infected with and spread the virus without knowing it.

Where does Canada stand on antibody testing?

In early May, Health Canada approved the first antibody test in the country. Developed by Italian multinational biotechnology company DiaSorin, the test was also approved for use in the U.S.

In a May 12 statement, Health Canada said at least one million Canadian blood samples will be tested for antibodies in the coming years.

“Understanding the scope and scale of COVID-19 infections across the country is key to managing the epidemic over the coming months,” the statement read. “This understanding will help inform public health decisions to protect the health of Canadians.”

More tests have since been approved, including a contract that is now in place between the federal government and Abbott Laboratories, which is producing 140,000 testing kits. Health Canada approved Abbott’s serology test on May 21.

A study in the Journal of Clinical Microbiology found only one false positive in more than 1,000 specimens tested with the Abbott tests.

A blood donor clinic pictured at a shopping mall in Calgary, Alta. on March 27, 2020.
A blood donor clinic pictured at a shopping mall in Calgary, Alta. on March 27, 2020.

Earlier this week, Canadian Blood Services announced they would begin testing around 37,000 samples in the coming weeks as part of a massive cross-country study to get a better picture of the disease.

Blood banks have been saving samples from people who have donated in recent months for testing. Donors will not be informed of their status, as the presence of antibodies does not require immediate medical attention.

“This is an opportunity for Canadian Blood Services and blood donors to contribute to the greater good, and create a strong foundation for evidence-informed decisions as we collectively navigate these unprecedented times,” Canadian Blood Services Centre for Innovation director Dr. Chantelle Pmabrun said in a statement.

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