ELISA stands for enzyme-linked immunosorbent assay.
ELISA tests can be used to detect the presence of antibodies to a specific antigen, for example, to test for infections by pathogens or for allergies. In this test, an enzyme is attached to antibodies. When this enzyme reacts with a certain substrate, a colored product is formed, causing the solution in the reaction vessel to change color. If a color change occurs, it indicates the presence of the antigen or antibody of interest.
Types of ELISA Test
There are two main types of ELISA tests:
- Direct Test: Uses a single antibody complementary to the antigen being tested.
- Indirect Test: Uses two different antibodies, primary and secondary.
An example of an indirect test is testing for antibodies, which can be used to identify if an individual has antibodies to HIV. In this test, HIV antigens are bound to the bottom of the reaction vessel. A blood plasma sample is then added to the vessel, and HIV-specific antibodies that are present bind to the antigens (primary antibodies). Any other antibodies present in the blood plasma are unbound and washed out. A second type of antibody with an enzyme attached is added to the reaction vessel (secondary antibodies). These secondary antibodies bind to the primary antibodies. The reaction vessel is washed out again to remove unbound secondary antibodies. A solution containing a substrate that reacts with the enzyme is then added. If secondary antibodies are present, a colored product is formed, indicating the presence of HIV-specific antibodies and therefore an HIV infection.
Another example of an indirect test is testing for antigens, which can be used to test for prostate cancer. This test involves testing blood plasma for the presence of prostate-specific antigens (PSA). If the PSA concentration of blood plasma is abnormally high, it suggests that the patient may have prostate cancer, and further tests can be carried out.
Diagram of Indirect Test Process
By using ELISA tests, clinicians and researchers can detect the presence of specific antigens or antibodies in patient samples, providing critical information for diagnosis and treatment.
