So in April, when the Pitkin County Public Health Department announced it had obtained 1,000 COVID-19 antibody tests that it would offer residents at no charge, it seemed like an exciting opportunity to evaluate the efforts underway to stop the spread of the virus.

Other ski towns such as Telluride, Colorado, and Jackson, Wyoming, as well as the less wealthy border community of Laredo, Texas, were also drawn to antibody testing to inform decisions about how to exit lockdown.

He and his team vetted 12 different antibody tests and found all but one turned up false positives — implying that someone had antibodies when they didn’t ― with false-positive rates reaching as high as 16 percent.

(Previously, companies were allowed to sell their tests without a review from the FDA, as long as they did their own validation and included a disclaimer.) And the American Medical Association said on May 14 that the tests should not be used to assess an individual’s immunity or when to end physical distancing.

The antibody tests instead parse the blood for antibodies against the COVID-19 virus.

So they first conducted their own validation tests, said Bill Linn, spokesperson for the Pitkin County Incident Management Team.

In Laredo, officials had been told by one of the community members helping to arrange the purchase of 20,000 tests from the Chinese company Anhui DeepBlue Medical Technology that they were FDA-approved, but the city’s own validation trials revealed only about a 20 percent accuracy rate, said Laredo spokesperson Rafael Benavides.

Before Laredo could pay for the tests, Benavides said, an arm of U.S.

In March, Covaxx, a company led by two part-time Telluride residents, offered to test residents of the town and the surrounding county with an antibody test it had developed.

The county is committed to doing a second round of testing but is evaluating how to proceed, said San Miguel County spokesperson Susan Lilly.

On May 4, the FDA updated its antibody test policy to require that manufacturers submit validation data, but it is still allowing the tests to be sold without the normal lengthy vetting and approval process, which includes demonstrating safety and effectiveness.

In Jackson, for example, a venture capitalist with an investment in Covaxx, the test used in Telluride, offered to help the city obtain 1,000 tests?

After Teton County officials decided against community antibody testing, a private nonprofit, Test Teton Now, sprung up to provide free COVID-19 antibody testing using the Covaxx test for roughly 8,000 people, about a third of the county’s residents.

The group has “done a lot” to verify the Covaxx tests, said Test Teton Now president Shaun Andrikopoulos?

Even a very accurate test will produce a large number of false positives when used in a population where few people have been infected.

If only 4 percent of people have actually been infected, a test with 95 percent accuracy would produce nine positive results for every 100 tests, five of which are false positives.