Ligand Displacement Immunoassay: A Novel Enzyme Immunoassay Demonstrated for Measuring Theophylline in Serum

surementof theophyllinein serum or plasma and show it to be clinicallyuseful.A conjugateof theophylline-specificanti-serum covalentlybound to micro-crystallinecelluloseand a-galactosidase-labeled theophyllinederivative is prepared as a lyophilizedreagent. Sample is added to the conjugate and, after 5-mm incubationat room temperature, the bound and displacedenzyme-ligand are separatedbybriefcentnfu-gation.The enzyme activityof the displacedenzyme-ligand is measuredon a spectrophotometeror centrifugalanalyzer. Linearcalibrationcurvesare obtainedwith appropriatesam-ple dilution,allowinggenerationof the standardcurvewith a saline zero reference and a single calibrator. Performance of the assay comparesfavorablywiththat of othertheophyllmne assays; comparisonstudies with use of 145 clinicalspeci-mens gave a coefficientof correlationwith EMITS of 0.97. AddItIonal Keyphrases: drug assay enzymic meth