The US Food and Drug Administration has issued its first emergency use authorization for a coronavirus test that looks for antibodies in the blood. That type of test, called a serology test, would be able to identify past coronavirus infections, although it may be less effective at identifying recent ones. The authorized test, from a manufacturer called Cellex Inc., requires blood to be collected through a vein, and the test itself can only be performed in a certified lab. Because antibodies can take time to develop, the FDA has previously warned against using antibody tests to definitively diagnose coronavirus. But in issuing what is known as an Emergency Use Authorization for the new test, the FDA signaled that the benefits of using the new blood test outweighed the risks. “Based on the totality of scientific evidence available to FDA, it is reasonable to believe that your product may be effective in diagnosing COVID-19,” said the agency, adding that “the known and potential benefits of your product when used for diagnosing COVID-19, outweigh the known and potential risks of your product.” Unlike most coronavirus tests, which generally require a swab and look for signs of the virus itself, antibody tests look instead for our body’s response to a virus. The FDA said in its letter that initial antibodies against coronavirus are “generally detectable in blood several days after initial infection,” but the agency cautioned that “levels over the course of infection are not well characterized.” The US Centers for Disease Control and Prevention says it is also working to develop a serology test – or blood test – that could look for antibodies, which would develop even in people with mild or no symptoms. Such tests can allow officials to better understand how prevalent coronavirus infections truly are, because they can identify people who had been previously infected but showed little or no symptoms. On Tuesday, a company called Bodysphere falsely claimed that an FDA Emergency Use Authorization was issued for an antibody test that could detect coronavirus in two minutes from a pinprick of blood. Multiple news outlets reported on the announcement, but later retracted their articles after the FDA confirmed that no such test had been authorized at the time. On Wednesday, the company acknowledged that the test had not in fact received the authorization. FDA guidance issued last month allows antibody tests to be manufactured and distributed without such authorizations. But any explicit authorization from the FDA – such as the one issued to Cellex – is a sign that regulators have confidence in a test’s validation data and believe its benefits outweigh its risks.