The FDA allowed an antibody test for COVID-19 to be marketed under Emergency Use Authorization, the agency said in a letter to the manufacturer on Thursday.

Cellex Inc. got the conditional OK for its qSARS-CoV-2 IgG/IgM RapidTest, designed to detect IgM and IgG antibodies in serum, plasma, or venipuncture whole blood, for CLIA-credentialed laboratories authorized "to perform moderate and high complexity tests."

In an interview with CBS Radio, FDA commissioner Stephen Hahn, MD, described this as "the first approval of a serology test, which will, in laboratories, allow us or allow the labs to determine exposure in the antibodies."

He noted that these tests are not "FDA-approved," but the agency is allowing manufacturers "to go forward as long as they've done their own quality assurance of those tests."

While the agency's letter to Cellex noted that "positive results for both IgG and IgM could occur after infection and can be indicative of acute or recent infection," the label made it clear this was to "aid in the diagnosis of patients with SARS-CoV-2 [the virus that causes COVID-19] infection in conjunction with clinical presentation and the results of other laboratory tests."

"Negative results do not preclude SARS-CoV-2 infection and should not be used as the sole basis for patient management decisions," according to the label.

The label also states, "False positive results for IgM and IgG antibodies may occur due to cross-reactivity from pre-existing antibodies or other possible causes. At this time, it is unknown for how long IgM or IgG antibodies may persist following infection."