While tests to detect COVID-19 are being developed and distributed at an unprecedented rate, demand is still exceeding supply. According to a recent analysis conducted by the Harvard Global Health Institute/Brown University School of Public Health for NPR, 4.4 million tests are needed in the U.S. every day to reach a basic level of proactive testing.1 One way to expand capacity is through utilizing antigen-based viral tests that can detect fragments of proteins found on or within the virus.
But what is an antigen test and how does it compare to the myriad of testing options out there? Here’s what you need to know.
What is an antigen and how does an antigen test work? An antigen is a molecule, such as a protein, that is foreign to your body and capable of causing your immune system to produce antibodies against it. An antigen test is used to detect the presence of foreign proteins, which are structural or functional components of a pathogen and are thus very specific to that pathogen. The test provides a qualitative “yes/no” answer on the presence of the pathogen in the patient sample. If the target antigen is present in sufficient concentrations in the sample, it will bind to specific antibodies and generate a positive result.2 Antigen tests have been around for years, offering healthcare providers with a way to rapidly diagnose medical conditions, such as strep throat or the flu, from the point-of-care within minutes.
What are the benefits of antigen tests? SARS-CoV-2 Antigen tests – which can be used as an alternative or in conjunction with molecular testing – can help provide a solution to one of the biggest challenges we’re facing today: scale. Antigen tests are relatively inexpensive and can help healthcare systems combat COVID-19 through increased testing in both the laboratory and at the point of care. Laboratory based antigen tests allow for cost and error reduction, as interpretation errors may be eliminated by automation, as well as fast turn-around times and high test throughput. Rapid tests, on the other hand, are beneficial in that they can be easily distributed throughout a community, including in non-traditional settings, such as schools, prisons, nursing homes and primary care offices, which could greatly benefit from access to testing at the point of care. Rapid antigen tests can also help to control the spread of disease in areas with high prevalence of the virus, with the quick turnaround time for results making them actionable in real-time. Within minutes of taking a test, a patient can self-quarantine, vs. waiting days for test results from a lab, and potentially infecting others during this time.
When should antigen tests be used? Antigen tests perform best when a person’s viral load is highest, typically at the early stages of infection when patients are symptomatic. These tests are particularly useful in congregate settings, such as schools or nursing homes, when rapid and repeat testing can help reduce the spread of the virus and protect vulnerable populations. In general, antigen tests have a high specificity, which is the test’s ability to correctly generate a negative result for people who don’t have the condition you are testing for. A high-specificity test will do a good job ruling out those who don't have the disease and won’t generate too many false-positive results. However, it is important to note that antigen tests are not as sensitive as PCR tests that amplify the target viral DNA or RNA sequence in order to generate a quantifiable signal to indicate the presence of the virus in a sample. Therefore, to make up for the potential decrease in sensitivity of an antigen test, negative results should be analyzed together with additional patient factors, such as COVID-19 exposure history, clinical symptoms, AND additional test results to help guide the diagnosis and treatment of the patient.
How do antigen tests fit into the current testing landscape? Across the globe, governments and healthcare systems are under intense pressure to increase testing capacity to help manage the spread of COVID-19. And while molecular testing remains the most reliable option in terms of accuracy, it is very hard to scale to pandemic levels. To address global needs, molecular tests need to be supplemented with other solutions that can more easily be produced and distributed en mass. Antigen tests can help fill this gap, as they can easily be deployed in communities or congregate settings where the virus is spreading, and deliver fast and actionable results, thus helping to increase testing capacity and slow the spread of the virus.
The ability to quickly and accurately identify a SARS-CoV-2 infection is critical to informing patient management decisions and helping to contain the spread of COVID-19. Roche remains committed to helping governments, healthcare professionals and patients fight COVID-19 through a variety of testing solutions in the laboratory and at the point of care.