A Critical Evaluation of a New Fluorescence Immunoassay System for the Measurement of Serum Phenytoin Concentrations

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Abstract
Results are presented which show that the Ames TDA™ phenytoin kit may be used with a shortened incubation time (5 minutes) and that, using a Fluorostat™ instrument, a single calibration curve can be stored and used effectively over a three-week period. The importance of temperature control when using a single calibration curve is emphasised. An unexplained finding was that higher results were obtained for phenytoin concentrations up to about 15 mg/1 with increasing incubation temperature. There was acceptable precision of measurement at all levels of phenytoin concentration, and there was no significant interference by haemoglobin, bilirubin, or lipids. The TDA results correlated well with those obtained using liquid chromatography (y=0·39 + 0·98x, r=0·98, where y=TDA and x=HPLC) and enzyme immunoassay (y=0·08 + 0·93x, r=0·96, where y=TDA and x=EIA).