COVID Antibody Tests, Useful For Gathering Data, Can't Yet Tell Whether A Person Has Immunity

May 14, 2020

Antibody tests are meant to detect whether a person has had a prior immune response to a COVID-19 infection. But the accuracy of the antibody tests on the market right now varies widely. Dr. David Grenache, Chief Scientific Officer for TriCore Reference Laboratories, spoke with Your NM Gov host Khalil Ekulona about how antibody tests are important from a population health perspective – to gather data about how many have been exposed – but they cannot tell us yet whether or not an individual has developed an immunity to the virus.

DR. DAVID GRENACHE: TriCore started offering its antibody test to the novel coronavirus a week ago yesterday. And given all the excitement, and frankly hype, about antibody testing, we expected to see a very large demand right out of the gate. But there hasn't been a large demand. So our test volumes have remains lower than I would have expected.

KUNM: There are a lot of different tests, depending on where you go. How accurate are your tests, and what is the predictive value of them?

GRENACHE: So right now, there are no antibody tests that have been formally approved by the FDA. There's none. But some manufacturers have taken their tests through this emergency use authorization pathway. And that does require the company selling the test to submit their data to the FDA. And if the FDA finds it acceptable, they will allow it to come to market through this emergency use authorization pathway. So at least there's some oversight and some signal to me, the laboratory professional, that there's some vetting of the test that has already happened prior to my evaluating the test. I would only offer a test that had gone through that emergency use authorization pathway.

KUNM: So we're saying, like, essentially, there's maybe a handful of emergency-authorized tests that are approved, yet there are hundreds of tests on the market.

GRENACHE: Exactly.

KUNM: And we have issues about the accuracy or the efficacy of those tests. Talk about how that is confusing to the consumer and what people should do to make sure that they get an approved test – one that is more likely to be accurate.

GRENACHE: No laboratory test is perfect, right. There will always be false results – either false positive or false negatives. But some tests do perform better than others, and when it comes to antibodies to the novel coronavirus, false results are concerning. So, right now, the usefulness of an antibody test result is really to identify a person who has had the novel coronavirus infection in the past. What we don't know yet is if the antibodies that our immune system makes actually lead to immunity. We don't know if the antibody response protects us in that way yet. So the value of an antibody test right now is rather limited. You know, you could have a false negative result: the test result says you don't have antibodies, but you actually do. And a false positive result would suggest to you that you did have the infection. And I'm afraid that that could lead some people to think that they are immune, and then not be so careful with social distancing and other safety practices that we've been taught to do.

KUNM: So regardless of your status – testing positive for antibodies or negative for antibodies – are you suggesting that no matter what test results you get back strictly at home, To the social distancing, and quarantining measures that many states are recommending,

GRENACHE: Yes. We can't yet rely on the antibody test results to change any safety practices, because we don't know the answer to that important immunity question yet.

KUNM: Roughly, how long do you think it will take for us to try to get an answer on that immunity question?

GRENACHE: Time has to go by for enough people who have actually already had the infection to get re exposed and not get sick again. That's the classic way of trying to determine if someone is immune. The other way, which is unethical, would be to take people who've had the infection and purposely expose them to the virus a second time. Those are really not an ethical way to conduct science.

*****

This originally aired on our show Your NM Government. Catch it every Wednesday, Thursday and Friday at 7:30 p.m. here on KUNM, or find it wherever you get your podcasts. Your NM Government is a collaboration between KUNM, New Mexico PBS and the Santa Fe Reporter.