Metabolite and matrix interference in phenytoin immunoassays

Metabolite and matrix interference in phenytoin immunoassays.

The major phenytoin metabolite, 5-(p-hydroxyphenyl)-5-phenylhydantoin glucuronide (HPPG), was primarily responsible for the positive bias noted when uremic specimens were assayed with the Abbott TDx Free Phenytoin fluorescence polarization immunoassay. The amount of bias depended on both HPPG and phenytoin concentration, increasing with increases in either concentration. The new Abbott TDx II a...

Screening for interference in immunoassays.

Screening for interference in immunoassays.

BACKGROUND The presence of interfering substances in patient samples submitted for immunoassay cannot be reliably anticipated. We therefore evaluated three interference screening techniques and estimated the prevalence of interfering substances as defined by positive outcomes with these protocols. METHODS We evaluated 160 samples for the presence of substances that may interfere with four imm...

Cross-reactivity of fosphenytoin in four phenytoin immunoassays.

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Cross-reactivity of fosphenytoin in two human plasma phenytoin immunoassays.

The cross-reactivity of fosphenytoin, a phosphate ester prodrug of phenytoin, was investigated in the Abbott phenytoin TDx/TDxFLx fluorescence polarization immunoassay (TDx) and the Behring Diagnostics phenytoin Emit 2000 enzyme-multiplied immunoassay (Emit). The first part of our study investigating cross-reactivity utilized in vitro correlation of the two immunoassays with a validated and spe...