What is Rapid Antigen Test for COVID-19?
The Rapid Antigen Detection Test (RADT) for COVID-19 is a rapid point-of-care nasopharyngel swab test that directly detects the presence or absence of coronavirus antigen in the patient’s body, generating diagnosis results within 30 minutes. These tests are designed to detect a specific protein in the virus that elicits the body’s immune response.
RT-PCR, though highly accurate, requires complex bio safety compliant set ups and takes longer to give a result. We are thus seeing longer turnaround times as the number of cases rise. The antigen testing solves this problem to an extent as apart from being fast, it is highly specific and thus positive results are highly accurate.
How does an antigen test work?
An antigen is a molecule capable of stimulating an immune response. They may be proteins, polysaccharides, lipids or nucleic acids. Each antigen has distinct surface features that are recognized by the immune system.
SARS-CoV-2, the virus that causes COVID-19, has several known antigens, including its nucleocapsid phosphoprotein and spike glycoprotein, which are the visible protrusions on its surface.
An antigen test reveals if a person is currently infected with a pathogen such as the SARS-CoV-2 virus. Once the infection has gone, the antigen disappears. Unlike nucleic acid based tests such as PCR, which detect the presence of genetic material, antigen tests detect proteins or glycans, such as the spike proteins found on the surface of the SARS-CoV-2. They usually provide test results rapidly, are relatively cheap, and can be more amenable to point-of-care use, which could make them more suitable for testing in the community and in remote regions.
Where will the Rapid Detection Test be used?
According to the ICMR, the antigen test may be performed under strict medical supervision in the following settings:
- In the containment zones to check the symptomatic influenza-like illnesses (ILI).
- In the containment zones to test asymptomatic high risk contacts of the confirmed cases with other chronic systemic illnesses within 5 to 10 days of contact.
- In healthcare settings, the antigen test may be used for people showing ILI symptoms, asymptomatic cancer patients, immunosuppressed individuals, elderly patients with other ailments and those undergoing dental procedures, non-surgical procedures like dialysis or surgeries which generate aerosol.
Can an Antigen Test diagnose the COVID-19?
The rapid detection test kit has been able to achieve 99.3% to 100% accuracy in detecting the true negativity. However, the specificity to discover the true positive is between 50.6% to 80%. Thus, testing must be done by maintaining the kit temperature between 2° and 30°C, and the kit will be used in containment zones or hotspots and hospital settings only.
How is the rapid antigen test different from Coronavirus Testing?
The significant difference between a Coronavirus Test and an Antigen Test is technology and time. For the diagnosis of COVID-19, RT-PCR test takes a minimum of 2-5 hours, including sample collection. On the other hand, a rapid antigen detection test (RADT) takes a maximum duration of 30 minutes for interpreting a positive or negative test.
What are the limitations of an antigen test’s results?
While the antigen test can be done in less time, it has certain limitations:
- The negative results from an antigen test may need to be confirmed with a molecular PCR test.
- Sample collection in the hospital setting is necessary. It cannot be used as a generalized test as claimed by many manufacturers.
Many laboratories and manufacturers, across the globe, are trying to develop testing kits, and scientists and researchers are working to develop the vaccination. However, people are advised to stay away from false claims and must follow the official channels and mediums to receive information.