Testing is an indispensable part of the effort to prevent and contain the SARS-CoV-2, the virus that causes COVID-19. The PCR test is the most known coronavirus test as it is considered to be the most accurate and reliable testing in identifying individuals with an active COVID-19 infection.
However, antigen and antibody tests were also developed to detect people who have the virus. With all these different types of tests for coronavirus, there will be confusion about its differences and purpose. In this article, we are going to explain the differences between these two tests and what they can tell us.
What are antibodies and antigens?
In the medicine industry, antibodies and antigens are often associated with illness and disease where it is said that they play a vital role in deciphering the type, cause, or treatment of the illness or disease. Antigens can make an individual unwell while antibodies are the substances that are used or produced by the body to defend itself from antigens.
To further elaborate, an antigen or immunogen is a molecule or substance that can stimulate an immune system response. They are usually bacteria or viruses and other substances from outside the body that can threaten the individual’s health. Each antigen has distinct surface features recognized by the immune system. The SARS-CoV-2 has several known antigens which are visible protrusions on its surface.
On the other hand, antibodies, also called immunoglobulins, are Y-shaped proteins made by B cells (a form of white blood cell) of the immune system in response to exposure to antigens. When an individual is infected with SARS-CoV-2, the body will produce antibodies that will bind specifically to the spike proteins and other antigens to eliminate the virus.
The binding can be harnessed and be used to develop antibody and antigen-based diagnostic tests.
What is an antigen test?
An antigen test can determine whether an individual is currently infected with a pathogen, such as the SARS-CoV-2 virus. Once the infection is gone, so will the antigen. This test is done by collecting a sample using a nasal or throat swab.
Unlike the PCR test that detects the virus’s genetic material, antigen tests detect proteins, such as the spike proteins found on the surface of the virus. Also, developing this kind of test takes longer than molecular and antibody tests as suitable antibodies for use in the assays must be identified and produced first.
The accuracy of the results might also be a problem with antigen tests as it has a lower sensitivity than PCR tests. However, they are cheaper to produce and provide rapid results in an hour or less. They are also more amenable to point-of-care use making them suitable for testing in various communities and even in remote places.
What is an antibody test?
Contrary to other tests for coronavirus that can tell if an individual is currently infected with the virus, an antigen test reveals the opposite. It can tell if a person has previously been exposed to the virus in the past by detecting antibodies in their blood or serum.
Antibody testing is done by a laboratory-based test such as enzyme-linked immunosorbent assay (ELISA), chemiluminescent immunoassay (CIA), or a point-of-care based on lateral flow technology.
As it can tell whether a person has already been infected with the virus, the test can give a more detailed representation of the COVID-19 pandemic situation. It can also help estimate how many people have already been infected with COVID-19 and therefore, is beneficial in assessing herd immunity.