Some antibody tests, which check for prior Covid-19 infection, had high rates of false positives in screenings performed by a consortium of California laboratories, according to a recently released report.

A false positive means someone would be told they’d already had coronavirus when they had not – a potential danger as people could then think they were immune to the virus when they’re actually still vulnerable.

Of the 12 antibody tests that were studied by the COVID-19 Testing Project, one of the tests gave false positives more than 15% of the time, or in about one out of seven samples. Three other tests gave false positives more than 10% of the time.

“That’s terrible. That’s really terrible,” said Dr. Caryn Bern, one of the authors of the study that looked at the 12 tests. She said while it’s unrealistic to think all tests will be 100% accurate all the time, their false positive rates should be 5% or lower, or ideally 2% or lower.

“This was a real wake up call for me. We’re not at the point where any of these tests can be used reliably,” added study coauthor Dr. Alexander Marson. “There’s a big danger in relying on them at all, but we hope we get to a point soon where we can rely on these tests.”

The COVID-19 Testing Project is a consortium of researchers and physicians at the University of California San Francisco, the University of California Berkeley, the Chan Zuckerberg Biohub, and the Innovative Genomics Institute.