An immunoassay is a
biochemicaltest that measures the concentrationof a substance in a biological liquid, typically serum or urine, using the reaction of an antibodyor antibodies to its antigen. The assaytakes advantage of the specific binding of an antibodyto its antigen. Monoclonal antibodiesare often used as they only usually bind to one site of a particular molecule, and therefore provide a more specific and accurate test, which is less easily confused by the presence of other molecules. The antibodiespicked must have a high affinity for the antigen(if there is antigenavailable, a very high proportion of it must bind to the antibody).
Both the presence of
antigenor antibodiescan be measured. For instance, when detecting infection the presence of antibodyagainst the pathogenis measured. For measuring hormonessuch as insulin, the insulinacts as the antigen.
For numerical results, the response of the fluid being measured must be compared to standards of a known concentration. This is usually done though the plotting of a standard curve on a graph, the position of the curve at response of the unknown is then examined, and so the quantity of the unknown found.
Detecting the quantity of
antibodyor antigencan be achieved by a variety of methods. One of the most common is to label either the antigenor antibody. The label may consist of an enzyme(see enzyme immunoassay(EIA)), radioisotopessuch as I-125 Radioimmunoassay(RIA), magnetic labels (magnetic immunoassay - MIA) or fluorescence. Other techniques include agglutination, nephelometry, turbidimetryand Western Blot.
Immunoassays have a particularly important role in the diagnosis of
HIVthrough the HIV test
Immunoassays can be divided into those that involve labelled reagents and those which involve non-labelled reagents. Those which involve labelled reagents are divided into homogenous and heterogeneous (which require an extra step to remove unbound
antibodyor antigenfrom the site, usually using a solid phase reagent) immunoassays. Heterogeneous immunoassays can be competitive or non-competitive.
* In a "competitive" immunoassay, the
antigenin the unknown sample competes with labeled antigento bind with antibodies. The amount of labeled antigenbound to the antibodysite is then measured. In this method, the response will be inversely proportional to the concentration of antigenin the unknown. This is because the greater the response, the less antigenin the unknown was available to compete with the labeled antigen.
* In "noncompetitive" immunoassays, also referred to as the "sandwich assay,"
antigenin the unknown is bound to the antibodysite, then labeled antibodyis bound to the antigen. The amount of labeled antibodyon the site is then measured. Unlike the competitive method, the results of the noncompetitive method will be directly proportional to the concentration of the antigen. This is because labeled antibodywill not bind if the antigenis not present in the unknown sample.
assaysdo not require this step, they are typically faster and easier to perform.
Lateral flow test
* Learning Guides from Abbott Laboratories on Immunoassay (English): [http://www.abbottdiagnostics.com/science/pdf/learning_immunoassay_01.pdf Part 1] [http://www.abbottdiagnostics.com/science/pdf/learning_immunoassay_02.pdf Part 2] [http://www.abbottdiagnostics.com/science/pdf/learning_immunoassay_03.pdf Part 3] [http://www.abbottdiagnostics.com/science/pdf/learning_immunoassay_04.pdf Part 4] [http://www.abbottdiagnostics.com/science/pdf/learning_immunoassay_appendices.pdf Appendix]
* [http://www.xiril.com/xiril/applications/elisapreparation/index.html Automation of Immunoassays]
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Look at other dictionaries:
Immunoassay — vgl. Immunassay … Das Wörterbuch medizinischer Fachausdrücke
immunoassay — [im΄yə nō as′ā, i myo͞o΄nōas′ā] n. [ IMMUNO + ASSAY] a technique for analyzing, and measuring the concentration of, antibodies, hormones, etc. in the body, used in diagnosing disease, detecting the presence of a tumor or drug, etc … English World dictionary
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immunoassay — noun Date: 1959 a technique or test used to detect the presence or quantity of a substance (as a protein) based on its capacity to act as an antigen • immunoassayable adjective … New Collegiate Dictionary
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immunoassay — noun A test for the presence of a substance using the reaction of an antibody to its antigen, making use of the high selectivity of components of biological immune systems … Wiktionary
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