Some antibody tests for COVID-19 previous infection can give false results, experts say

Some antibody tests which aim to determine if a person has already been exposed to, and has recovered from, COVID-19, can give false results, experts say.
WESTMINSTER, Calif. (KABC) -- It's hard to miss: A big white tent in the Westminster Mall parking lot off the 405 Freeway.

It's the Covid Clinic. According to spokesman Matt Collins, it's a partnership by Sean Penn's nonprofit Community Organized Relief Effort, or CORE, and Huntington Beach family practice Dr. Matthew Abinante.

For $125, a person can get a nasal swab test for COVID-19., For $75 you can take an antibody test.

If you test positive for the antibody, it means you likely had the virus in the past and have recovered.

People here have waited in their cars as long as six hours in line to be tested.

My photographer and I decided to take the antibody test. We went around 1 p.m. on a Thursday afternoon when the line was no more than a couple cars long at most.

One reason I was really interested in taking this test is my husband actually came through here. He tested positive for the antibody so I thought there was a chance I probably had it too.

We weren't allowed to record inside the tent, but after a finger prick and about a 10-minute wait, my results were in.

"You came back negative for the IgG and the IgM," one of the staff members at the clinic told me through my car window.

Negative.

I was really disappointed.

I definitely thought that I probably had had it at some point because my husband's test came back positive for the IgG.

Regardless of anyone's test results, we knew we had to proceed with caution because we don't know enough about COVID-19 or how accurate this test was. There was no guarantee at this time my husband couldn't be reinfected even if he did carry that antibody.

I spoke with Saahir Khan, an assistant clinical professor who specializes in infectious disease at the University of California at Irvine.

Khan said maybe I didn't get COVID-19, which would be odd if my husband did have it at some point.

"Amongst household contacts, we see a fairly high rate of transmission," Khan said.

Maybe my husband never had COVID-19.

"Potentially, the husband's test could've been a false positive. There are other coronaviruses that cause the common cold," Khan explained.

Khan pointed out a lot of the tests out there look for antibodies that develop with several viruses within the coronavirus group - not just the strain causing this pandemic, SARS-CoV-2.

The manufacturer insert for the test kit used here states this:

Positive results may be due to past or present infection with non-SARS-CoV-2 coronavirus strains.

Then it lists four other strains this test can react to: Coronavirus HKU1, NL63, OC43 OR 229E.

"Sometimes you can have antibodies to the virus that cause the common cold that could potentially cross-react with this test," Khan said.

This IgG test is not FDA approved, but on its website, the manufacturer of the test provides a letter from the FDA acknowledging receipt of an application for Emergency Use Authorization.

The spokesperson for the clinic admitted the test has its limitations and we don't know enough about the virus to tell people they are immune if they test positive for the antibody.

"We don't tell patients that have a positive reading that they can go to normal life or stop practicing social distancing. We believe that would be irresponsible at this time until we have more knowledge of the virus," Collins said.

But the form handed to those with a positive result for this antibody states:

"You now have antibodies for the disease. The chances of you contracting COVID again are probably very close to 0%."
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