SARS-CoV-2 Antigen Tests Disadvantages

Less sensitive than PCR assays.Antigen tests are not as sensitive as PCR tests, and false negatives can cause real problems.A negative antigen test should always be considered presumptive,but still gives patients and caregivers a false sense of security.These tests may not be appropriate in settings where positive results cannot be missed, such as hospitals or settings with high-risk patients or staff.While this type of testing occurs less frequently, false positives are also problematic and can lead to major workflow issues within healthcare facilities, and for the public to miss days at work and school.

• Fewer expert interpretations in point-of-care settings.Despite the convenience of point-of-care testing,it is important to remember that this test is often performed and interpreted by healthcare professionals who are not trained in clinical laboratory science. Appropriate messaging around interpretation of results is imperative, including the potential for false negative and false positive results, and continued use of public health measures, such as masking and distancing, is essential.

• Evidence on performance and use is limited.There is little literature discussing the assay performance of COVID-19 antigen assays. Guidance on the use of these tests in a pandemic setting may be limited.

• Laboratory space, supplies and personnel are still required. Just because an antigen test can be done faster than most PCR tests doesn't mean it can be used outside of a certified laboratory or without proper training. Additionally, 2 of the 3 antigen tests that have received Emergency Use Authorization (EUA) from the U.S.Food and Drug Administration (FDA) require the use of their manufacturer's automated system, and doing so will require laboratories to purchase new instrumentation and supplies do not yet own these systems.

Limitations

Test performance was determined only in symptomatic patients.The presentation of asymptomatic patients is unknown.Use of viral transport media may result in decreased test sensitivity.This is important to consider as nasopharyngeal swabs are often collected in viral media.Also, if viral transport media is not used, it should be shipped to the laboratory as quickly as possible.False negative results may occur if the swab is not swirled in the second well before closing the test card, if insufficient extraction buffer volume is used (eg, < 6 drops) and if the test is performed > 1 hour after collection.Also, the presence of mupirocin may interfere with the test and possibly cause false negative results.