Education Education Elucidation 115 Oct 2020 21:56
Utilizing Antibodies and Antigens in Diagnostics
When infected with a pathogen such as SARS-CoV-2, the body produces antibodies that bind specifically to the antigens to help eliminate the pathogen. This binding can be harnessed to develop antibody and antigen-based diagnostic tests.
Antibody vs Antigen Testing for COVID-19
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Antibody vs Antigen Testing for COVID-19
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An antibody test reveals if a person has already been exposed to an infection, by detecting antibodies in their blood or serum. This can be done by a laboratory based test such as an ELISA (Enzyme-Linked Immunosorbent Assay) or CIA (chemiluminescent immunoassay), or a point-of-care test based on lateral flow technology.
Antibody tests are not usually used to diagnose current infection as it takes the body some time to produce antibodies. During the period before the adaptive immune system kicks in, the fast-acting and non-specific innate immune response combats infection. A negative test result may occur if the test is taken too soon after infection before antibodies have been produced by the body. False positive test results could also occur due to cross-reactivity.
Antibody tests are useful to help track the spread of a disease, identify those who should be prioritized for vaccinations, and highlight potential donors for convalescent plasma therapy.
An antigen test reveals if a person is currently infected with a pathogen. 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, such as those found on the surface of a virus. Accuracy can be a problem, with antigen tests typically having a much lower sensitivity than PCR.
However, 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.
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