ELISAEnzyme-Linked Immunosorbent Assay(ELISA) is a sensitive, heterogenous (multiple phase) analytical technique for quantitation of antigen or antibody in which enzyme-labeled antibody or antigen is bound to a solid support (e.g., tubes, beads, microtiter plate wells, plastic tines or fins). After addition of patient specimen and substrate, antigen, antibody or complex are detected by a color change indicating the presence of the product of an enzyme-substrate reaction. Direct ELISA is a technique for measuring antigen using competition for antibody binding sites between enzyme- labeled antigen and patient antigen. Indirect ELISA, or enzyme immunometric assay, measures antibody concentrations using bound antigen to interact with specimen antibodies. Enzyme-labeled reagent antibodies can be isotype-specific (i.e., capable of determining the presence of IgG, IgA, IgM or IgE classes which react with the antigen of interest). The specificity of indirect ELISA assays for IgM isotypes in some infectious diseases is limited by false-positive results due to IgM rheumatoid factor in the presence of IgG-specific antibodies.
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