Performance Characteristics of a New Levetiracetam Immunoassay and Method Comparison With a High-Performance Liquid Chromatography Method

BACKGROUND: Although levetiracetam is recognized for ease of dosing and being well tolerated, therapeutic drug monitoring is potentially useful in certain clinical situations. High-performance liquid chromatography has been commonly used for measuring levetiracetam. Recently, a homogeneous immunoassay for levetiracetam measurement in serum and plasma was introduced by ARK Diagnostics, Inc. The goal of this work was to validate this assay on a random access instrument. DESIGN AND METHODS: This immunoassay was established on the Siemens ADVIA 1200 automated chemistry analyzer. The intraday precision was assessed by 10 replicates of two levels of quality control materials in a batch, whereas interday precision was estimated by assaying the same materials one set per day for 20 days. Linearity was evaluated by serially diluting the highest calibrator and a high patient specimen run in triplicate, whereas the lower limit of quantification was confirmed by 10 measurements of a low-level specimen diluted from a calibrator and another from a diluted patient specimen. This method was compared with a commercial high-performance liquid chromatography method (Chromsystems) using 63 specimens from patients who were on levetiracetam therapy. RESULTS: The assay cycle was 10 minutes with a theoretical throughput of 800 per hour. The intra- (n = 10) and interday (n = 20) coefficients of variation were 8.1% or less for the two levels tested. The manufacturer-claimed analytical measurable range (2.0-100.0 μg/mL) was confirmed by serial dilution and lower limit of quantification experiments. Among the 63 patient samples studies, four showed levetiracetam levels below 2.0 μg/mL by both methods. Deming regression using the remaining 59 paired patient results by ARK immunoassay and the high-performance liquid chromatography method showed a correlation coefficient of 0.9962, a linear regression slope of 0.98, and an intercept of 0.61 with a mean bias of 0.04%. CONCLUSION: The ARK immunoassay is suitable for clinical use of monitoring levetiracetam levels in serum/plasma on an automated chemistry analyzer (Siemens ADVIA 1200).