Since the inception of COVID-19 pandemic, testing has become a very vital part of the response provided. Standard PCR tests have helped detect the virus in people with the current infection, but there are several antibody and COVID-19 antigen swab test that are still in the lab. We dedicate this article to examining the difference between these tests and the information we can get from them.
Antigens and antibodies; what are they?
Antigens are molecules that can stimulate a response in the immune system. They may be polysaccharides, lipids, proteins, or nucleic acids. Each of these antigens has unique features on their surfaces which allows them to be identified by the immune system.
The virus SARS-COV-2 is the cause of COVID-19. This virus has many antigens which include spike glycoprotein and nucleocapsid phosphoprotein. These two antigens are visible as protrusions on the surface of the virus.
Antibodies are proteins with Y shape and are produced by the B cells of the immune system when it is exposed to antigens. These Y-shaped arms have tips which act as binding sites (paratopes) for the antigens. These parotopes bind to a particular part on the surface of the antigen called the epitope. This binding is what enables the elimination of these antigens from the body. It works either by tagging for the other arms of the immune system to eliminate or by direct neutralisation.
When people contract SARS-COV-2, their bodies produce antibodies that bind to the spike proteins and some other antigens to eliminate the virus. It is from this binding that the development of diagnostic tests based on antibodies and antigens seems reasonable.
What is an antibody test?
An antibody test is used to check for signs of exposure to an infection in people by detecting some specific antibodies in their serum or blood. This is achievable through laboratory tests like enzyme-linked immunosorbent assay (ELISA), or chemiluminescent immunoassay (CIA), or a point-of-care test which is dependent on lateral flow technology.
Antibody tests are not dependable for diagnosing current infections. This is because it may take a while for the body to produce antibodies after an exposure. Usually, before the body produces antibodies through the adaptive immune system, it will first try to combat the infection with a rapid non-specific innate response.
According to the data on SARS-COV-2, the response by IgM antibody is most active after two weeks of contracting the infection, before the IgG comes in the third week.
What information can we get from an antibody test?
With the antibody test, we can detect how far the disease has spread and even go as far as tracking it, thereby achieving a more accurate representation of the impact of the COVID-19 pandemic. It can provide information on the number of people that have contracted SARS-COV-2, and this can be very helpful when assessing herd immunity.
This antibody test can differentiate between the IgM and IgG, thereby providing information on the current phase of the infection. Reports from this can help health workers know how long a person has been carrying the disease. This test can help identify people who should be placed in compulsory vaccination as soon as they are available and those that should consider being donors for the convalescent plasma therapy.
Antibody tests; the limitations
The primary limitation of this test is the same with others; the testing method may not always give correct results.
When the test is taken too soon, the result will be negative since the antibodies are yet to be produced. People can also get a false-positive result as the test could detect antibodies that were developed for the previous infection with other types of coronavirus.
Proper care must be employed when interpreting the result for this test. For COVID-19, it is not yet sure if antibodies will prevent people against future infections from SARS-COV-2. If this is so, the duration for the protection will also need to be ascertained. This could allow the issuance of immunity passport to identify individuals that are immune and safe to go back to work.
However, research shows that the antibodies decrease after two months, thereby reducing the window for detecting people that have been previously infected.
Available antibody tests for SARS-CoV-2
Some antibody tests are available, and they include those developed by Roche, Beckman-Coulter, Abbott, and EUROIMMUN.
What are the antigen tests, and what information can we derive from them?
Antigen tests are used for examining a person for a current infection from pathogens like SARS-COV-2. The test is not useful after the infection is gone since the antigen disappears immediately after the infection.
This test detects proteins or glycans, which are found on the surface of SARS-COV-2 instead of the PCR test, which detects genetic materials. Developing this test can take a longer time than the antibody and molecular tests since the assay requires proper identification and production of some suitable antibodies.
However, since they are cheap, they can be used at a point-of-care and can produce rapid test results, they are suitable for tests in remote areas.
Available antigen tests for SARS-CoV-2
The available antigen swab test is the one developed by Qiudel. The rest are still under development.
For your antigen swab test in London, you can contact www.walkinclinic.london today!