Dry-reagent strips for measuring phenytoin in serum.

A new reagent strip has been developed for measuring phenytoin in serum or plasma. It utilizes the chemistry of the Apoenzyme Reactivation Immunoassay System (ARIS) and is designed for use with the Seralyzer reflectance photometer. The 90-s test relies on comparison of strip reactivities with a two-point calibration line, which can be validly stored in the instrument for two weeks. Within-run CVs for controls at five concentrations ranged from 2.7 to 5.6%, between-run CVs from 2.3 to 6.3%. Phenytoin values obtained for clinical serum samples correlated well (r greater than 0.99) with those obtained by liquid chromatography or substrate-labeled fluorescent immunoassay. The speed and convenience of this assay for monitoring phenytoin in serum make it well suited for decentralized test sites such as emergency rooms, urgent-care centers, and physician's offices.