Radioimmunoassay heterogeneous immunoassay

Most immunoassays currently employed in the biomedical field are either radioimmunoassays, enzyme immunoassays, or luminescence immunoassays (including fluorescence immunoassays [FIA] and chemiluminescence immunoassays). Although radioimmunoassay is currently the most sensitive of these (10 -10 M concentrations are often detectable), due to the problems inherent to dealing with radioactive materials, such as licensing, radiation hazard, short shelf-life of expensive radioisotopes, the expense of the counting equipment, and the tedium associated with heterogeneous immunoassay, it has fallen, in popularity, behind the non-isotopic methods of analysis. 

Enzymes are currently the most widely used and investigated labels for immunoassays, because a single enzyme label can provide multiple copies of detectable species. This catalytic amplification results in immunoassay detection limits that rival those of radioimmunoassay without the storage and disposal problems associated with radioisotopes. Enzyme immunoassays label either ligands or antibodies with enzyme, and enzyme activity in bound or free fractions is measured. Heterogeneous immunoassays employing enzymatic labels have been named enzyme-linked immunosorbent assays (ELISAs). ELISA methods usually employ antibody immobilized onto the wells of polystyrene microtiter plates, and may be... 

Samples from patients receiving digoxin therapy were analyzed by the heterogeneous immunoassay LCEC method. Samples were diluted 5/1 with pooled human plasma in order to eliminate an observed antibody matrix effect. Digoxin standards in pooled human plasma were treated similarly and a standard curve constructed. Digoxin levels in patient samples were determined by reference to the standard curve. The values obtained for the samples by the electrochemical enzyme immunoassay method were compared to those obtained by radioimmunoassay. The results for the 54 samples analyzed are presented in Fig. 8. A good correlation was obtained between the two methods (r = 0.93). 

Radioimmunoassay A heterogeneous immunoassay in which the label is a gamma or beta emitter. 

Methods for detection of anti-dsDNA include immunofluorescence, hemagglutination, radioimmunoassay (RIA), and enzyme-linked immunoassay (ELISA). Different methods may result in discrepant results due to the heterogeneous nature of the antibodies (S20). Numerous studies that compare methods conclude that no single test is perfect. It may be necessary to combine different methods for both higher sensitivity and higher specificity. The most commonly used methods for detecting anti-dsDNA are the CLIF test, the Farr assay, and the ELISA test. 

The heterogeneous enzyme immunoassays, which include the enzyme-linked immunosorbent assay (ELISA), are based on the same principles as are used in radioimmunoassays (RIA). In short, after incubation of antigen and antibodies, the antigen-antibody complexes formed are separated from free antigen and antibody by one of a number of different techniques, and the activity in one or both of the fractions is determined. 

The development of enzyme immunoassays was pioneered in 1972 by Engvall and Perlmann " and by Van Weemen and Schuurs and is translated into a wide variety of enzyme-based systems used both in research and in routine analysis with sensitivities approaching those of radioimmunoassays. Enzyme immunoassays (EIAs) can be divided into two major classes, homogeneous and heterogeneous. 

Heterogenous fluorescence immunoassays can be carried out with the aid of the same separation procedures used in radioimmunoassay. The more expedient homogenous fluorescence immunoassays require quenching, enhancement, polarization, or shifting of the fluorescence of the label upon binding of the labeled analyte to its antibody. Occasionally, a second antibody, directed at the anti analyte antibody, will be used in a double-antibody method to precipitate the bound labeled and unlabeled analyte or to alter the optical properties of the label in such a way as to make the analysis more sensitive. 

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