Generally, antigen tests are indicated for the qualitative detection of SARS-CoV-2 antigens in authorized specimen types collected from individuals suspected of COVID-19 by their healthcare provider within a certain number of days of symptom onset, according to a news release.
However, the FDA is aware of reports of false-positive results associated with the antigen tests when used in nursing homes and other settings, and it said it is monitoring and evaluating these reports, along with other relevant and available information about device safety and performance.
The administration noted that laboratories should expect some false-positives to occur, even with very accurate tests, but the labs and healthcare providers should follow authorized instructions from the CDC, including routine follow-up testing with a molecular assay when appropriate.
Additionally, the FDA recommends that laboratory staff and healthcare providers who use antigen tests for rapid COVID-19 detection be aware of conditions of the emergency use authorization (EUA) that specify the manufacturer’s instructions, including stipulations such as appropriate times to read the results and ways to handle test cartridges/cards.
Multiple specimens in batch mode could make it more challenging to ensure the correct incubation time, too, while cross-contamination is a risk that can be caused by insufficient cleaning, disinfection or inappropriate use of protective equipment (such as failing to change gloves between patients).
The CDC recommends that, when using antigen tests in nursing homes and other settings, it may be prudent to follow positive results with confirmatory RT-PCR tests within 48 hours.
FDA said it continues to work with other agencies, including the CDC and CMS to safeguard COVID-19 test use in nursing homes and other settings. Additionally, the administration is working with manufacturers to ensure that instructions are clear and will continue to update those involved of new or additional information.