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What Is an ELISA Assay?

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  • Written By: Karize Uy
  • Edited By: Lauren Fritsky
  • Last Modified Date: 24 November 2016
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An ELISA Assay is a testing process that detects substances in order to identify certain diseases, allergies, and illegal drugs in the body. It is also known to be used to detect human immunodeficiency virus (HIV). Some of the substances it can detect are antibodies, hormones, and proteins. The main principle behind the ELISA assay is that a chemical reaction between a patient’s liquid sample and a specific laboratory sample indicates the presence of a certain substance associated with a specific disease or medical condition. ELISA, as an acronym, stands for “enzyme-linked immunosorbent assay.”

The invention and development of the ELISA assay came about because there was a need for a safer testing method other than the radioimmunoassay, which uses radioactivity to produce a chemical reaction. In the 1960s, two separate groups of scientists spearheaded by Stratis Avrameas and G.B. Pierce became successful in partnering certain antibodies with certain enzymes and producing a chemical reaction from the combination. With this knowledge at hand, two scientists from Stockholm University, Peter Perlmann and Eva Engvall, invented the ELISA method, publishing their experiments and the system behind the assay in 1971. Since then, the ELISA assay has been used worldwide, although the radioimmunoassay is still available due to its lesser cost.

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There are two common types of ELISA assay: the direct and the indirect method, the latter being more commonly used. The first step would be to extract a sample from the patient, usually blood or urine, both of which may undergo a separating process to extract the clear serum containing the antibodies. An ELISA kit often contains a plate that holds 96 mini-containers called “wells,” which will be coated with an antigen that can possibly have a reaction to a present antibody. An antigen is often considered a foreign substance that the body attacks by producing specific antibodies, so if a patient has acquired an antigen from a certain disease, his serum should contain antibodies that correspond to the said antigen.

The patient’s serum will then be poured in the wells and then incubated to let the antibodies adhere to the protein coating. After the incubation period, the wells are rinsed off to remove the rest of the serum and other antibodies that have not bound to the coating. Another set of antibodies extracted from animals, usually rats, will be poured in the wells to detect the human antibodies, and another incubation period takes place and the animal antibodies will be washed off again. An enzyme substrate will then be added so the reaction can be visibly seen in colors. Typically, a strong shade of color will indicate a positive result, which means the patient does have the disease or other medical conditions tested for.

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