The U.S. Food and Drug Administration (FDA) on Tuesday warned people against the use of unauthorized versions of certain COVID-19 rapid antigen tests currently being marketed in the United States.

These tests have not been authorized, cleared or approved by the FDA for distribution or use in the United States, the health agency said, adding that they may show false results.

The warning was issued against unauthorized versions of Celltrion USA Inc's DiaTrust COVID-19 Ag Rapid Tests, SD Biosensor Inc's STANDARD Q COVID-19 Ag Home Test, and ACON Laboratories' Flowflex SARS-CoV-2 Antigen Rapid Test.

The authorized versions of the tests can continue to be used, but consumers should compare the packaging to make sure they do not buy unauthorized tests, the FDA said.

The unauthorized Acon test comes in blue packaging, SD Biosensor in a white and magenta box and Celltrion's in green and white packaging, according to the agency.

The FDA has not received reports of injuries, adverse health consequences or death associated with the use of these unauthorized tests.

All three companies have initiated a recall for all unauthorized tests that were distributed in the United States.

Antigen tests require a nasal or throat swab and can produce results more quickly than molecular tests, which detect genetic material in the virus. However, antigen tests are considered less accurate.