The US Food and Drug Administration will now require antibody test makers to promptly seek FDA authorization, as the agency aims to rein in unproven and fraudulent tests that have flooded the market.

The new policy, announced Monday, requires commercial manufacturers to submit emergency authorization requests, along with validation data for their antibody tests, within 10 business days. The FDA is also setting specific performance recommendations for all test developers.

The agency also said it has the capability, working with the National Cancer Institute, to independently validate antibody tests on the market.

The move to require authorization reverses a policy the FDA put in place in mid-March, which loosened approval standards and allowed companies to sell antibody tests, also known as serological tests, without providing evidence that the tests worked.

With the coronavirus spreading across the US, the aim was to get antibody tests on the market. But the decision was a trade-off, FDA officials acknowledged, and putting the priority on early access to antibody tests came at the expense of assurances that the tests were reliable.

“We are continuing to adapt our approach based on real-world experience and data and so, as FDA has authorized more antibody tests and validation data have become available, including through the capability at NCI, the careful balancing of risks and benefits has shifted from where it was in mid-March,” said FDA Commissioner Dr. Stephen M. Hahn. “This has all informed the changes to our policy regarding antibody tests.”

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Antibody tests are used to check for prior Covid-19 infection and can provide a better sense of how much of the population has already been infected and might have some immunity to the virus. It’s still not clear whether the presence of antibodies means someone is immune or how long that immunity might last.

But as companies rushed to market after the FDA’s March announcement, it quickly became clear that many of the tests were unreliable. A number of tests had high rates of false positives, which could give people a false sense of security by leading them to believe they have already been infected and have immunity from the virus.

Other companies marketed tests that they falsely claimed were FDA-approved or FDA-authorized. Some companies falsely claimed the antibody tests could be used to diagnose Covid-19 or could be used for at-home testing.

“We unfortunately see unscrupulous actors marketing fraudulent test kits and using the pandemic as an opportunity to take advantage of Americans’ anxiety,” wrote Dr. Anand Shah, the FDA’s deputy commissioner for medical and scientific affairs and Dr. Jeff Shuren, the FDA’s director of the Center for Devices and Radiological Health.

The two FDA officials wrote, “flexibility never meant we would allow fraud.”

By also moving to independently validate antibody tests, the FDA will have better data to decide whether to authorize the test, work with the test developer to sort out fixes for the test or block the test from marketing in the US.

If commercial manufacturers who are currently marketing tests fail to submit EUA approvals, “we intend to share this information publicly,” Shah and Shuren wrote.

The move comes after House Democrats raised concerns last month about inaccurate antibody tests, noting that FDA officials admitted at the time that the agency wasn’t able to validate tests that were on the market.

An FDA official stressed that all antibody tests have limitations and should only be used with experts who understand the tests. The tests should be taken into account along with clinical symptoms and prior diagnostic testing, the official said. Without those factors, it may be prudent to use two antibody tests, according to FDA officials.

To date, at least 10 antibody tests have been authorized under an individual EUA, most within just the past few days, and over 200 antibody tests are currently the subject of a pre-EUA or EUA review.