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An assay that quantifies antigen or antibody by immunochemical means. The antigen can be a relatively simple substance such as a drug, or a complex one such as a protein or a virus. See Antibody, Antigen

The reactants are first mixed so that a varying quantity of one (A) is added to a constant amount of the other (B). The formation of an immune (antigen-antibody) complex is measured as a function of the varied reactant (A). The result is represented by a “standard curve” for reactant A. An unknown sample is tested by adding it to reactant B. The extent of the measured change is referred to the standard curve, and thereby is obtained the amount of reactant A which produces a comparable change. The amount is represented as the content of reactant A in the unknown sample. See Immunofluorescence, Immunology, Radioimmunoassay


A laboratory detection method that uses antibodies to react with specific substances.
References in periodicals archive ?
Moreover, because of poor protein binding of digoxin-like immunoreactive components of ginseng, elimination of this interference in the FPIA assay by monitoring free digoxin in the protein-free ultrafiltrate is not possible.
Effect of Ginseng Supplementation to Digoxin Pools on Serum Digoxin Measurement by Immunoassays Digoxin Concentration, Mean (SD), mg/mL * Specimen and Type of Ginseng FPIA ECLIA-Digoxin Digoxin pool 1 2.
Within-method variation was again lowest for the FPIA assay; the mean CV was 4.
To confirm the observation that tHcy values obtained by the FPIA method were lower at increased tHcy concentrations compared with values obtained by HPLC-FD (TBP/SBDF), we reanalyzed each of the 10 pools by both methods over 10 days.
Our analysis of tHcy values obtained on five pools analyzed in two of three surveys showed that only the FPIA method (CV, 4.
Lastly, heptaminol was added to drug-free urine specimens to determine the response of the AxSYM FPIA assay for amphetamines.
06%) with the AxSYM FPIA Amphetamine/Methamphetamine II assay, but gives false-positive results only with high urine concentrations of heptaminol.
Response of AxSYM FPIA assay for amphetamines after addition of heptaminol to drug-free urine.
We can also exclude that the higher MEGX concentrations observed in uremic patients were the result of positive interferences with the TDx FPIA by substances that had accumulated in uremic plasma because the predose (0 min) value was subtracted from values obtained at the various postinjection times.