A Covid-19 blood test is administered outside of Delmont Medical Care on April 22, in Franklin Square, New York. Al Bello/Getty Images

The US Food and Drug Administration has authorized three new coronavirus antibody tests, bringing the total number of FDA-authorized tests to seven.

The tests were green-lit under emergency-use authorizations, a lower regulatory standard used when the FDA believes a test’s benefits could outweigh any risks.

Three companies – DiaSorin, Ortho-Clinical Diagnostics and Autobio Diagnostics – received the authorizations. The tests were restricted to use in authorized laboratories, and the FDA cautioned that all three came with risks of false positives and negatives.

The tests would ideally allow for the detection of past infections – indicating if someone has had the virus, regardless of whether they showed symptoms. But the tests may be less useful for diagnosing recent or current infections.

“A negative result may occur if you are tested early in your illness and your body hasn’t had time to produce antibodies to infection,” the FDA wrote in fact sheets accompanying the tests.

Some context: The agency’s new authorizations come amid growing questions over the role of antibody tests in the coronavirus pandemic.

The FDA has come under congressional scrutiny for allowing manufacturers to distribute antibody tests without authorization, a move that triggered a flood of shoddy tests in the US market.

And it remains unclear whether antibodies – even when detected by high-quality tests – indicate that someone is immune to re-infection.

“There is no evidence yet that people who have had Covid-19 will not get a second infection,” the World Health Organization warned in a recent scientific brief.