The U.S. Food and Drug Administration is warning that a coronavirus test that Los Angeles officials have offered to tens of thousands of residents for free since spring can produce "the risk of false results, particularly false negative results."

The test is administered by Curative, which produces 10% of the nation's daily tests and has administered over 11 million tests. The company operates the largest testing site in the country at Dodger Stadium. The year-old company run by Fred Turner has grown quickly and acquired contracts with the Air Force. It also tests members of Congress and is used by several major cities.

To reduce the false results, the FDA warns to test "symptomatic individuals within 14 days of COVID-19 symptom onset."

But in Los Angeles and elsewhere, the company often tests non-symptomatic individuals. L.A. Mayor Eric Garcetti said he had hoped that making the tests widely available would reduce the spread of the virus. His office did not reply to repeated requests for comment.

The FDA did not indicate how frequently incorrect test results were produced, but according to Curative's own non-peer-reviewed studies, it has a false negative rate at around 10%.

Turner has argued that the rate is better than most of the nasal swab testing out there and oral tests, which can be self-administered, are the only way the country can reopen quickly.

But the FDA warns that false negative tests can lead to consequences like delayed treatment and lack of monitoring of infected individuals, which could lead to an increased risk of spreading the virus.

The agency said a negative result from Curative "does not rule out COVID-19 and should not be used as the sole basis for treatment or patient management decisions."

The Los Angeles company was originally created to detect sepsis but pivoted to COVID testing efforts early last year.

"We have been working with the agency to address their concerns and these limitations, and we will continue to work interactively with FDA through the Emergency Use Authorization process," Curative spokesman Pasquale Gianni said in an emailed statement.

He added: "Curative's test has been validated and is being offered during the pandemic under an Emergency Use Authorization, and is labeled with specific warnings, precautions, and limitations that FDA reiterated in the Safety Communication. The test performance and labeling, however, have not changed, nor has the company observed any changes in test performance."

In a press conference Thursday afternoon, Garcetti reiterated that the FDA's guidance does not impact the tests' use on symptomatic people, and defended the city's testing of asymptomatic individuals, saying that one-third of people who test positive for COVID are asymptomatic.

"This test is used by both symptomatic and asymptomatic people in countless jurisdictions, by the United States Congress, by NBA," he said. "Let's be clear about what the FDA said: For people with symptoms, they didn't issue any further guidance. It works. There's no issues. And that's been two thirds of all the tests."

He added that the false negative test rate in asymptomatic individuals is similar to other tests.

"What the FDA guidance says, like any test, is that you have to do it and use it correctly," he said. "So I'll remind people, if you're going to use this test, you have to cough, vigorously, three to five times."

It is unclear what prompted the warning from the FDA. Officials there did not respond to requests for comment, but it did not alter Curative's emergency use permit.