7 things to know about COVID-19 antibody testing

As more people recover from the novel coronavirus and seek to resume their normal activities, there’s been a lot of talk about testing for COVID-19 antibodies.

But what are antibody tests, exactly, and how do they differ from diagnostic tests for COVID-19? What do the results indicate for the people who take these tests? And what do they mean for how we should conduct ourselves during the COVID-19 pandemic?

To learn more about COVID-19 antibody testing, we spoke with Micah Bhatti, M.D. Here’s what he had to say.

What is antibody testing, and how does it differ from diagnostic testing used for COVID-19?

Diagnostic testing for COVID-19 involves looking to see whether an active virus is present — in this case, the coronavirus formally known as SARS-CoV-2. Laboratory technologists use a testing process to detect genetic material from the virus in samples swabbed from the very back of the nasal cavity. This testing is based on a common molecular testing technique: polymerase chain reaction (PCR).

By contrast, antibody testing (also called serology testing) is done with blood samples, because you’re looking for evidence of the body’s immune response to the virus.

After your body is exposed to a foreign pathogen, your white blood cells start to learn about it and make antibodies to neutralize it. So, when an antibody test comes back positive for this coronavirus, it means 1) you were exposed to SARS-CoV2 at some point in the past and 2) your immune system was robust enough to launch an antibody-forming immune response.

How long does it usually take people to generate these antibodies?

There are limited data related to antibodies against SARS-CoV2. Some reports suggest most healthy people start making antibodies 11 to 14 days after symptoms first appear.

But there are also other variables to consider, such as malnourishment, having cancer or another chronic health condition, or taking immune suppressing drugs. All of these can affect people’s ability to make antibodies.

What does a positive coronavirus antibody test result mean for someone in terms of immunity?

The short answer is we don’t know.

It may mean someone has full immunity or partial immunity or no immunity at all. Some antibodies decrease over time, so you might be immune for six months to a year, and then maybe not at all later on. Or, it might be like a tetanus immunization, where if you get it once, you’re most likely immune the rest of your life. There’s just no way to give definitive answers right now.

How long will it take before we know for sure what positive COVID-19 antibody test results really mean?

The answer to that question will take lots of research, and probably at least a year of data collection, to figure out. Because first, you need to find people with the COVID-19 antibody. Then, you need to follow them to see if they become infected again if they’re exposed to the virus in the future. And that takes time.

Why is it important for people not to assume they’re immune if they test positive for COVID-19 antibodies?

There’s a big difference between telling someone they have immunity versus that they may have immunity. That’s a really important distinction to make.

Because if someone says that they’re definitely going to give me a million dollars, I may go out and buy a new house. But if they tell me they may give me a million dollars, I probably won’t, because it’s not a promise. It’s only potential.

With this virus, we just don’t know the answer yet. We can only advise patients that they may have immunity if the antibody test is positive. So, even if I were to test positive for antibodies to the coronavirus, I wouldn’t change my behavior. I’d still wear personal protective equipment at work, wash my hands a lot and practice social distancing.

How accurate are the tests currently available?

The jury is still out on how good serology tests are for this coronavirus. They’re not used widely enough to have good answers yet.

A lot of companies are trying to market their tests right now. And some are making false claims to the point that the Food and Drug Administration may have to take action. It’s important to note that just because someone is saying they have a serology test, doesn’t necessarily mean you can trust that test to provide accurate results.

Here at MD Anderson, we’re looking at bringing in serology tests from some of the bigger, more established diagnostic equipment suppliers. We’re hoping to have those available in the coming weeks.

Where can people obtain antibody testing? And who should?

At MD Anderson, an antibody lab test requires orders from a physician. Antibody testing primarily reveals if you were exposed to SARS-CoV2 in the past and generated an antibody-forming immune response.

Until we know how antibody test results relate to immunity, the tests are mainly useful for epidemiologists and researchers. But as always, you should discuss your medical needs and any questions with your physician.

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• Recovered from COVID-19? 4 things to know
• COVID-19 herd immunity: 7 questions, answered
• What counts as COVID-19 exposure?

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