Rapid Antigen Testing (RAT) for COVID-19
Since the beginning of the pandemic, diagnostic devices based on nucleic acid amplification techniques, such as the real-time polymerase chain reaction (RT-PCR) tests, have been extensively used in the diagnosis of COVID-19. However, as we start to reopen public spaces and return to our daily lives, public access to more convenient, affordable, and faster testing options has grown critical.
Rapid antigen tests for COVID-19 have recently become available in the form of point-of-care (POC) tests and self-tests. By eliminating the need for laboratory equipment and extensive training for the preparation, application, and the interpretation of the test, rapid antigen testing has enabled a quick, affordable, and convenient way to check for a SARS-COV-2 infection on the spot. The availability of rapid antigen tests also helps reduce the stress on healthcare workers, prevent the overcrowding of hospitals, and lower the overall costs. Thanks to its immense utility for public health, rapid antigen testing proves to be an excellent complement to molecular testing methods such as PCR.
How SARS-CoV-2 Rapid Antigen Tests Work
In a nutshell, SARS-CoV-2 rapid antigen tests are rapid chromatographic immunoassays for the qualitative detection of SARS-CoV-2-specific proteins, or antigens, present in human nasal, nasopharyngeal, or saliva samples. This technology has been already utilized for the detection of a wide range of pathogens including strep, influenza, malaria, and HIV.
Unlike molecular testing such as PCR, rapid antigen tests do not detect viral genetic material. Instead, this technique involves the use of series of special antibodies to detect proteins specific to the investigated pathogen. Consequently, while a molecular test requires laboratory equipment and healthcare professionals for its application, procession, and interpretation; rapid antigen tests can be performed outside of a laboratory setting with minimal training. Moreover, while molecular tests may take up to a few days to deliver results, with rapid antigen tests, the results are usually ready within minutes.
SARS-CoV-2 rapid antigen tests primarily target the predominantly expressed structural proteins of the virus such as the nucleocapsid protein or the spike protein.
SARS-CoV-2 rapid antigen tests typically use a sandwich immunodetection method in lateral flow test format. After the sample is transferred to the assigned well on the test strip, the liquid flows along the surface of the kit through capillary flow. If the virus is present, a line of labeled mobile antibodies will bind to viral antigens in the sample and form antigen-antibody complexes. As the sample continues to flow, these antigen-antibody complexes migrating along the surface of the test strip and are captured by another line of immobilized antibodies. Consequently, the label of the captured antigen-antibody complexes appears as a colored line on the test strip. If the test is positive, both the control line (C) and the test line (T) will be visible after 15 to 30 minutes. If the test is negative only the control line (C) will appear. If the control line (C) does not appear at all, the test result is considered invalid.
Rapid antigen testing (RAT) as Point-of-Care Tests
As point-of-care tests, rapid antigen testing facilitates regular widespread screening in minimum time. As these tests can be conducted anywhere by minimally trained personnel, they can be used in various community and occupational settings. On one hand, rapid antigen tests can easily be utilized for the early detection of cases in resource-limited or remote areas where PCR testing might not be readily available. In the absence of PCR testing, screening by rapid antigen tests has proven to be a highly effective strategy for the detection and isolation of positive cases in high prevalence settings. In fact, even within low prevalence settings where confirmatory testing may be required to rule out the possibility of infection, the sensitivity of rapid antigen tests has proved sufficient for the detection of highly infectious patients.
On the other hand, rapid antigen testing has a clear advantage over PCR testing when receiving rapid results has critical importance. Thus, this method can be efficiently used for isolation and contact tracing purposes. As the results are instantly available, these tests enable rapid screening, immediate isolation, and access to care.
Rapid antigen tests can also be used in educational settings, industrial settings, offices, airports, and other institutions to facilitate regular surveillance. In such contexts, rapid antigen tests can be easily and quickly distributed, applied, processed, and interpreted.
Rapid antigen testing (RAT) as Self-Tests
As self-tests, rapid antigen testing allows people to test themselves wherever, whenever, and as frequently as they might need. Whether you want to attend a crowded gathering, visit someone at-risk, check yourself after close contact, or just assure yourself, taking a rapid antigen test may inform you in minutes at the comfort of your own home.
If you test positive, you can take immediate action, self-isolate, and inform your contacts to curb the spread of the virus. On the other hand, if you take a test negative immediately before an event, gathering, or visit, it is very likely that you are not currently infected by SARS-COV-2, and even more likely that you are not infectious. Indeed, while negative rapid antigen tests may require additional testing to completely rule out the possibility of infection, rapid antigen tests demonstrated excellent accuracy in detecting infectious amounts of viral load. Moreover, if you do not have access to PCR testing, you can perform routine antigen testing to confirm your infection status. It has been proven that the rapid antigen tests perform just as well as a single PCR test when an antigen test is taken every three days.
Where can I buy the SARS-CoV-2 Rapid Antigen Test Kit?
COVID-19 antigen tests are available online as well as at pharmacies, doctors’ offices, and certain retail establishments. In the United States, complimentary rapid antigen test kits can be mailed to your home by the United States Postal Service. You may also find rapid antigen test kits on retailers such as CVS, Walmart, and Target, or buy one online on Amazon. Rapid antigen test kits are widely accessible in pharmacies, supermarkets, and online throughout the European Union. In Germany, for example, supermarkets such as Aldi, Lidl, and Edeka, as well as drugstores such as Rossmann, provide rapid antigen testing. Furthermore, if you are a registered patient in the medical system, many pharmacies and testing institutions provide low-cost rapid antigen tests. You can buy these tests without a prescription and use them regardless of your medical condition.
- Jüni P, Baert S, Corbeil A, et al. Use of rapid antigen tests during the omicron wave. Science Briefs of the Ontario COVID-19 Science Advisory Table. 2022;3(56). https://doi.org/10.47326/ocsat.2022.03.56.1.0