Companies usually turn to the firm PeopleG2 to run background checks on employees. Now, they can use PeopleG2 to buy up blocks of COVID-19 tests to see if workers have developed immunity to the disease.

PeopleG2 is one of several companies that are selling a type of test that detects COVID-19-fighting antibodies in less than 15 minutes. These tests are part of a confusing landscape of antibody tests for sale online, most of which have not been authorized by the U.S. Food and Drug Administration.

A spokesperson for the FDA told Fast Company over email that these tests don’t necessarily need explicit FDA approval as long as they meet certain criteria. In an update published this week, the FDA notes that antibody tests, also called serology tests, are an important facet of identifying people who have overcome the virus. This information can help determine who might be able to return to work and who might be a good candidate for blood donation.

To help these testing efforts ramp up, the FDA is allowing test developers to market and sell their tests once they have followed certain guidance set out by the FDA to assess accuracy and reliability. The tests are only allowed to be administered in a healthcare setting, since at-home testing has not been sanctioned. “The FDA issued this policy to allow early patient access to certain serological tests with the understanding that the FDA has not reviewed and authorized them,” the agency notes.

ToxTest, a company that sells employee drug testing supplies, is among the companies that are currently selling rapid-result antibody blood tests for COVID-19. ToxTest’s tests were created by W.H.P.M. Inc., a company that creates FDA-approved medical devices. On its website the company says that its test is 97.9% accurate, though it has not been reviewed by the FDA. W.H.P.M Inc. also specifies that its test is for “professional use only,” perhaps a designation aimed at deterring non-clinical use. PeopleG2 also sells antibody tests online from several different test purveyors, including Advin Biotech, a company that has been developing rapid diagnostics since 2009.

Both PeopleG2 and ToxTest are selling packages of 25 antibody tests for between $625 and $650, or roughly $25 per test. Both tests use a finger-prick blood sample and yield results in less than 15 minutes, and neither have FDA approval. The only antibody test the FDA has approved under an emergency use authorization is a test from Cellex Inc.

Despite coming from established companies that appear to be following guidelines, both Assistant HHS Secretary Admiral Brett Giroir and Dr. Deborah Birx, who is coordinating the response to the coronavirus, have expressed concern about unvalidated tests. “Most of them have not been approved by the FDA,” said Giroir during a Wednesday interview on Fox and Friends. “The FDA, CDC, NIH are trying to validate all the tests that are out there that we know about to make sure that they really perform.”