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Candidate reference method for determining serum theophylline applied to target-setting in external quality
L M Thienpont1, B Van Nieuwenhove, D Stöckl
1Laboratoria voor Medische Biochemie en Klinische Analyse, University of Ghent, Belgium.
Clinical Chemistry
|August 1, 1994
Summary
A new isotope dilution gas chromatography-mass spectrometry method offers precise serum theophylline measurement with minimal bias. This validated method accurately assesses routine assays, identifying performance variations in clinical settings.
Area of Science:
- Clinical Chemistry
- Analytical Chemistry
- Pharmacokinetics
Background:
- Accurate serum theophylline measurement is crucial for therapeutic drug monitoring.
- Existing routine assays may exhibit variability and bias.
- A high-quality reference method is needed for assay validation.
Purpose of the Study:
- To develop and validate a candidate reference method for serum theophylline determination.
- To evaluate the performance of three routine theophylline assays against the reference method.
Main Methods:
- Isotope dilution gas chromatography-mass spectrometry (ID-GC-MS) with extractive alkylation.
- Method bias, imprecision, and total error were quantified.
- Linear regression analysis was used to compare the reference method with routine assays.
Main Results:
- The candidate reference method demonstrated excellent precision (CV 0.63%) and low bias (< 1.0%).
- Maximum total error was less than 2.1%, indicating high accuracy.
- The TDx II and Emit 2000 assays showed good to excellent performance, while the Kodak Ektachem assay exhibited significant bias and dispersion.
Conclusions:
- The proposed ID-GC-MS method is a reliable reference standard for serum theophylline quantification.
- Routine assay performance can vary, necessitating validation against accurate reference methods.
- The findings aid in selecting appropriate assays for clinical theophylline monitoring.