PETINIA Total Phenytoin Assay on the Vista 1500 Analyzer Is Not Suitable for Monitoring Free Phenytoin Concentration if Ultrafiltration Is Performed at Room Temperature

Dasgupta, Amitava; Everett, Jamie; Davis, Bonnette

doi:10.1097/ftd.0b013e318288449a

Cited by 2 publications

(1 citation statement)

References 16 publications

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“…8 Regression results reported for a Siemens Vista 1500 method (Siemens, Tarrytown, NY) were: Vista=0.852*TDx + 0.066; r 2 =0.81. 9 A scatter plot ( Figure 3) of residuals comparing our method to the FP TDx assay did not reveal discernable bias between methods throughout the assay range. Within-run CV based on mean and standard deviation of 13 measurements 3.8%, and between-run CV, assessed with 49 measurements in separate runs over a 2-week period, was 5.5%.…”

Section: Figurementioning

confidence: 81%

An Automated Real-Time Free Phenytoin Assay to Replace the Obsolete Abbott TDx Method

Williams

Jones

Akl

et al. 2014

Lab Med

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Phenytoin is a commonly used anticonvulsant that is highly protein bound with a narrow therapeutic range. The unbound fraction, free phenytoin (FP), is responsible for pharmacologic effects; therefore, it is essential to measure both FP and total serum phenytoin levels. Historically, the Abbott TDx method has been widely used for the measurement of FP and was the method used in our laboratory. However, the FP TDx assay was recently discontinued by the manufacturer, so we had to develop an alternative methodology. We evaluated the Beckman-Coulter DxC800 based FP method for linearity, analytical sensitivity, and precision. The analytical measurement range of the method was 0.41 to 5.30 microg/mL. Within-run and between-run precision studies yielded CVs of 3.8% and 5.5%, respectively. The method compared favorably with the TDx method, yielding the following regression equation: DxC800 = 0.9**TDx + 0.10; r2 = 0.97 (n = 97). The new FP assay appears to be an acceptable alternative to the TDx method.

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Section: Figurementioning

confidence: 81%

An Automated Real-Time Free Phenytoin Assay to Replace the Obsolete Abbott TDx Method

Williams

Jones

Akl

et al. 2014

Lab Med

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Possible False-Negative Results on Therapeutic Drug Monitoring of Phenytoin Using a Particle Enhanced Turbidimetric Inhibition Immunoassay in a Patient With a High Level of IgM

Hirata

Saruwatari²,

Enoki

et al. 2014

Therapeutic Drug Monitoring

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: In this report, the authors described the unusual case of a patient in whom the plasma phenytoin concentration was unexpectedly not detected on a particle-enhanced turbidimetric inhibition immunoassay (PETINIA) technique, a typical immunoassay for phenytoin. The plasma concentration was measured using PETINIA and high-performance liquid chromatography in a 69-year-old male patient treated with fosphenytoin intravenously at the standard dose for 7 days. Although the plasma concentration of phenytoin was below the limit of detection (<0.5 mcg/mL) on PETINIA after the administration of fosphenytoin, the trough plasma concentration was estimated to be between 5 and 10 mg/L on high-performance liquid chromatography. When the plasma concentrations of IgM and IgG were measured using an enzyme-linked immunosorbent assay, the plasma IgG level was within the reference range, whereas the plasma IgM level was 2-3 times higher than the upper limit of the reference range. We concluded that the PETINIA method yielded a possible false-negative result regarding the phenytoin level in this patient, perhaps because of some hindrance to the measurement process by IgM. This case suggests that false-negative results should be considered when therapeutic drug monitoring reveals abnormally low values using PETINIA and that it is necessary to evaluate the plasma IgM level.

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PETINIA Total Phenytoin Assay on the Vista 1500 Analyzer Is Not Suitable for Monitoring Free Phenytoin Concentration if Ultrafiltration Is Performed at Room Temperature

Cited by 2 publications

References 16 publications

An Automated Real-Time Free Phenytoin Assay to Replace the Obsolete Abbott TDx Method

An Automated Real-Time Free Phenytoin Assay to Replace the Obsolete Abbott TDx Method

Possible False-Negative Results on Therapeutic Drug Monitoring of Phenytoin Using a Particle Enhanced Turbidimetric Inhibition Immunoassay in a Patient With a High Level of IgM

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