title: Candidate reference method for determining serum theophylline applied to target-setting in external quality assessment and routine method evaluation.
abstract: We present a candidate reference method for the determination of serum theophylline by isotope dilution gas chromatography-mass spectrometry, using extractive alkylation in sample preparation. The maximum method bias was < 1.0%. The mean method imprecision (CV) was 0.63% (range 0.37-0.96%), calculated from the results of six measurements independently performed on 3 days. The maximum total error of the method, including the method bias and 95% confidence interval, was < 2.1%. Investigation of various substances and metabolites for interference proved the specificity of the proposed method. The method was used to evaluate three routine assays by linear regression analysis. Performance of the TDx II (Abbott) was excellent and of the Emit 2000 (Syva) assay was good. The Kodak Ektachem assay showed a high dispersion of results and a pronounced positive bias in the subtherapeutic range.
authors.affiliation: Laboratoria voor Medische Biochemie en Klinische Analyse, University of Ghent, Belgium.
authors.forename: L M
authors.initials: LM
authors.lastname: Thienpont
authors.forename: B
authors.initials: B
authors.lastname: Van Nieuwenhove
authors.forename: D
authors.initials: D
authors.lastname: Stöckl
authors.forename: A P
authors.initials: AP
authors.lastname: De Leenheer
mesh_terms: D005069:Evaluation Studies as Topic; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D006801:Humans; D007201:Indicator Dilution Techniques; D011786:Quality Control; D011933:Reagent Kits, Diagnostic; D012044:Regression Analysis; D012680:Sensitivity and Specificity; D013806:Theophylline / Q000097:blood*
chemical_list: D011933:Reagent Kits, Diagnostic; D013806:Theophylline