Enzyme Immunoassay

Commonly abbreviated “EIA,” this widely used laboratory technique also goes by the name of “Enzyme-linked Immunosorbent Assay” (ELISA). Blood donor infectious disease screening relies heavily on EIA. These tests are both highly sensitive and specific, the perfect combination for blood donor screening. In simplest form, EIA utilizes a bound substance that is supposed to attract a target substance in the donor’s blood (a so-called “capture reagent”). For example, if we were screening for the presence of an antibody such as anti-HIV-1,2, the test manufacturer would bind the target antigen to a test well (this can and is done in reverse, with bound antibodies detecting blood/plasma antigens). If antibody were present in our donor’s sample, it would be expected to bind to the antigen and as a result, be bound to the well of the test kit. Detection of the bound substance occurs through the addition of an anti-human antibody that carries a bound enzyme. Finally a chromogenic substance (the target of the enzyme) is added and the resultant color change from the enzymatic reaction is detected and compared to negative controls. Chemiluminescent immunoassays (ChLIA) are similar, but the chromogenic substance and enzyme reaction is replaced by a reaction that gives off visible light.

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