We evaluated three commonly used clinical methods for measuring serum methotrexate: enzyme immunoassay (EMIT), radioassay, and radioimmunoassay. Because potentially interfering compounds can be resolved by liquid chromatography, this method was selected as the comparison method. Patients' serum samples, taken during 24 h after 6-h high-dose infusions, contained methotrexate in concentrations ra...

The antiepileptic drugs diphenylhydantoin and phenobarbital were measured in serum by a new commercially available enzyme immunoassay procedure ("EMIT," Syva Corp.). The procedure requires less than 5 min and no more than 50 mul of serum per determination. It is simple; only four steps (pipetting and diluting with an automatic pipettor-dilutor) are required before spectrophotometry. Twenty repl...

A homogenous enzyme immunoassay for the quantitative determination of netilmicin in serum was developed. The procedure utilizes a commercially available assay for gentamicin (EMIT; Syva Co., Palo Alto, Calif.). The method was adapted to a microcentrifugal analyzer, and log-logit regression analysis was performed with a computer. The results of samples assayed by this method correlate well with ...

A homogeneous substrate-labeled fluorescent immunoassay has been applied to the measurement of phenytoin concentrations in human serum. We coupled a fluorogenic enzyme substrate, galactosyl-umbelliferone, covalently to a derivative of phenytoin. Under assay conditions, this drug-substrate conjugate was nonfluorescent but became fluorescent upon hydrolysis catalyzed by bacterial beta-galactosida...

A commercial kit for determining immunoreactive insulin, the “Phadebas Insulin Test,” was methodically evaluated to establish the optimal conditions for this immunoassay. Sensitivity, day-to-day and withinrun precision, recovery, accuracy, and specificity are excellent. Results by this method compare favorably with those of the double-antibody technique. This rapid, simple, convenient, and reli...

We describe a "fluorescence protection immunoassay," in which formation of an immune complex of a fluorescer-labeled antigen sterically protects the fluorescer from binding by antibodies to it. Competitive binding of unlabeled antigen by its antibody prevents formation of the fluorescer-labeled antigen immune complex, and allows anti-fluorescein to quench the fluorescence by binding to the fluo...

A homogeneous enzyme immunoassay (EMIT) for serum thyroxine determination has been evaluated. It was also compared to our routine method, a radioimmunoassay with use of a commercial kit, Tetra-Tab RIA. Within-day precision was very similar for the two methods, the CV ranging from about 2.5% at 150 nmol of thyroxine per liter to about 5.7% at 25 nmol/L. The two methods were compared by running 1...