Antigen tests are less expensive to produce than PCR tests and can be performed very quickly, making them an option worth considering as a screening tool. This may help reduce the testing burden in some regions once more reliable antigen tests come to market. While molecular testing is possible in real time, supply chain and throughput challenges have made this impractical during the COVID-19 pandemic. Implementing antigen testing in the COVID-19 testing algorithm could reduce pressure on laboratories and preserve molecular testing for situations requiring high test sensitivity.
The advantages and disadvantages of SARS-CoV-2 antigen testing need to be considered to determine if and when it is a reliable method for COVID-19 diagnosis.
advantage
Antigen testing is cheap and fast. Knowing that molecular testing cannot continue to carry the burden of all acute COVID-19 testing in the United States, antigen testing offers a solution to the need for tests that can be produced cheaply and run quickly.
Antigen testing may be a useful public health tool. Because antigen tests are generally considered very accurate when positive, they may be useful in quickly identifying highly infectious individuals within the community. However, it is important to note that antigen test performance may be poor in areas of low disease prevalence, and there are limited data on test performance in asymptomatic individuals. Because antigen tests are more likely to be positive when a person has a higher viral load, superspreader events or outbreaks can be prevented by identifying these people early and putting them into isolation.
Potential for use in point-of-care settings. The rapid nature of antigen testing and the low reliance on expensive equipment and reagents make it ideal for point-of-care testing. This can reduce the testing burden on laboratories and provide rapid results where patients are tested. It's important to note that point-of-care sites must have a CLIA certificate to run these tests, so locations where they can be offered will vary.
shortcoming
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, as well as the public missing days at work and school.
Expert interpretation in the point-of-care setting is less frequent. 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 have no training in clinical laboratory science. Appropriate messaging around the interpretation of results, including the potential for false-negative and false-positive results, and the continued use of public health measures such as masking and distancing are 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.
