Ligand displacement immunoassay: a novel enzyme immunoassay demonstrated for measuring theophylline in serum.
We describe a ligand displacement immunoassay for measurement of theophylline in serum or plasma and show it to be clinically useful. A conjugate of theophylline-specific antiserum covalently bound to micro-crystalline cellulose and a beta-galactosidase-labeled theophylline derivative is prepared as a lyophilized reagent. Sample is added to the conjugate and, after 5-min incubation at room temperature, the bound and displaced enzyme-ligand are separated by brief centrifugation. The enzyme activity of the displaced enzyme-ligand is measured on a spectrophotometer or centrifugal analyzer. Linear calibration curves are obtained with appropriate sample dilution, allowing generation of the standard curve with a saline zero reference and a single calibrator. Performance of the assay compares favorably with that of other theophylline assays; comparison studies with use of 145 clinical specimens gave a coefficient of correlation with EMIT of 0.97.
D000925:Anticoagulants / Q000097:blood; D002986:Clinical Trials as Topic; D003429:Cross Reactions; D006801:Humans; D007124:Immunoenzyme Techniques; D007700:Kinetics; D008024:Ligands; D012996:Solutions; D013806:Theophylline / Q000097:blood*; D001616:beta-Galactosidase
D000925:Anticoagulants; D008024:Ligands; D012996:Solutions; D013806:Theophylline; D001616:beta-Galactosidase