The ELISA has a variety of applications in the medical field; it is particularly useful for tests on the liquid part of blood (serum), due to the fact that it can be used to detect either the presence of an antibody or the presence of the antigen itself. It is commonly used as one part of the HIV test, although a variety of different types of tests are usually used in conjunction when testing for HIV in a sample or patient. It can similarly be used to detect the West Nile virus, and is actively used to diagnose lyme disease, pernicious anemia, RMSF, rotavirus, squamous cell carcinoma, syphilis, and other diseases.
The ELISA is a very sensitive test, which makes it very useful for early medical screenings. This is because the test relies on a marker enzyme, which is attached to an antibody that detects the presence of a pathogen (or the presence of another antibody). After the application of this special antibody, the plate containing the samples is washed; thus the antibody and enzyme will only remain if the pathogen (or antibody) being tested for is present. Even a small amount of the marker enzyme will cause the catalysis which produces a visual result in the form of a color change; the color change will be more pronounced based on the amount of antigen present in the sample, up to a point at which the change in color plateaus. Thus, the test can detect very small amounts of an antigen in a sample, and can even subjectively or comparatively determine amounts of antigen in a sample. Because of the subjective nature of the color change, however, it can be difficult to determine at what point a result should be classified as positive and at what point it is a negative result. Thus the ELISA is usually used in the medical field as a preliminary test to determine whether further testing should be done, but is not usually considered sufficient to declare a final positive result without further testing.
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“Enzyme-Linked Immunosorbent Assay (ELISA) Technique.” Biobest. Biobest Laboratories Ltd, n.d. Web. 08 July 2016. <http://www.biobest.co.uk/diagnostics/techniques/elisa-how-does-the-test-work.html>.