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FDA Warns of Potential False Positives With Rapid SARS-CoV-2 Antigen Tests

NEW YORK – The US Food and Drug Administration released a letter Tuesday warning laboratories and healthcare providers about the potential for false positive results with rapid antigen tests for detecting SARS-CoV-2.

The letter noted that not following the instructions for use for antigen tests can lead to inaccurate results, especially if samples aren't taken from patients within a certain timeframe after symptom onset. According to the agency, "laboratories should expect some false positive results to occur even when very accurate tests are used for screening large populations with a low prevalence of infection."

The agency recommended multiple actions for SARS-CoV-2 rapid antigen test users, including remaining aware that laboratories should follow the instructions for use when performing the test and reading the results – specifically with regards to appropriate storage of test components and reading the results in the appropriate time.

The FDA also noted that processing multiple specimens in batches could make it more difficult to ensure proper intubation time for each sample and emphasized the importance of minimizing the risks of cross-contamination when testing samples, by properly cleaning workspaces and instruments and using protective equipment correctly. 

For patients in certain settings, including nursing homes, the agency recommends performing confirmatory RT-PCR testing on positive results within two days.

Currently, seven rapid antigen tests for detecting SARS-CoV-2 have received Emergency Use Authorization from the FDA. Some have called for increased use of such tests for mass testing in the US for the coronavirus, but some studies have called into question the sensitivity of the tests, which lag behind PCR tests.

Last week, the FDA updated its template for the development of rapid antigen-based SARS-CoV-2 tests to include recommendations concerning data and information that should be submitted to the agency to support EUA applications.