Antigen tests, a new category, have a major advantage and disadvantage over COVID-19 tests already approved.
Late last week, FDA approved the first antigen test for COVID-19 as well as the first diagnostic test with the option of using home-collected saliva samples.
FDA issued the first emergency use authorization (EUA) for a COVID-19 antigen test, a new category of tests. The Sofira 2 SARS Antigen FIA (Quidel Corporation) is authorized for use in high and moderate complexity laboratories certified by Clinical Laboratory Improvement Amendments (CLIA), as well as for point-of-care testing by facilities operating under a CLIA Certificate of Waiver.
The antigen tests quickly detect fragments of proteins found on or within the virus by testing samples collected from the nasal cavity using swabs, FDA said in a press release.
To date, FDA has approved polymerase chain reaction (PCR) tests, a molecular diagnostic testing technique that detects the genetic material from the virus and can help diagnose an active COVID-19 infection. It has also cleared serological tests that look for antibodies to the virus.
PCR tests can be incredibly accurate, but running the tests and analyzing the results can take time.
"One of the main advantages of an antigen test is the speed of the test, which can provide results in minutes. However, antigen tests may not detect all active infections, as they do not work the same way as a PCR test,” the FDA said.
While antigen tests are very specific for the virus, they are not as sensitive as molecular PCR tests.
“This means that positive results from antigen tests are highly accurate, but there is a higher chance of false negatives, so negative results do not rule out infection,” the FDA said. “With this in mind, negative results from an antigen test may need to be confirmed with a PCR test prior to making treatment decisions or to prevent the possible spread of the virus due to a false negative.”
Antigen tests can generally be produced at a lower cost than PCR tests and, once multiple manufacturers enter the market, can potentially scale to test millions of Americans per day due to their simpler design, “helping our country better identify infection rates closer to real time,” FDA said.
Meanwhile, FDA issued an emergency use authorization (EUA) to Rutgers Clinical Genomics Laboratory for its COVID-19 laboratory developed test (LDT), to permit testing of samples self-collected by patients at home using the Spectrum Solutions LLC SDNA-1000 Saliva Collection Device.
“Authorizing additional diagnostic tests with the option of at-home sample collection will continue to increase patient access to testing for COVID-19. This provides an additional option for the easy, safe and convenient collection of samples required for testing without traveling to a doctor’s office, hospital or testing site,” according to FDA Commissioner Stephen M. Hahn, MD, in a press release.
“The Rutgers Clinical Genomics Laboratory test is currently the only authorized COVID-19 diagnostic test that uses saliva samples to test for SARS-CoV-2, the strain of coronavirus that causes COVID-19. The test remains prescription only,” the FDA said.
The Rutgers test allows testing of a saliva sample collected from the patient using a designated self-collection kit. Once patients collect their saliva sample, they return it to the Rutgers Clinical Genomics Laboratory in a sealed package for testing.
However, FDA’s authorization is limited to testing performed at the Rutgers Clinical Genomics Laboratory using its molecular LDT COVID-19 authorized test for saliva specimens collected using the Spectrum Solutions LLC SDNA-1000 Saliva Collection Device.
Read more: FDA expedites coronavirus testing kits