title: Comparability and imprecision of 8 frequently used commercially available immunoassays for therapeutic drug monitoring.
abstract: BACKGROUND
  The development of new immunoassays for therapeutic drug monitoring and the adaptation of current assays on new analytical platforms has led to a plethora of different tests. This variability may influence comparability between the methods and affect interpretation of test results used for guiding drug treatment.
  
  
  METHODS
  Comparability and imprecision of 8 immunoassays for therapeutic drug monitoring were evaluated using 6 different analyzers from 3 manufacturers. Current and previous generation analytical systems used were Architect and AxSym (Abbott Laboratories), cobas c 501 module and COBAS INTEGRA 800 analyzer (Roche Diagnostics GmbH), and Dimension Vista and Dimension Xpand (Siemens Healthcare Diagnostics Inc). Carbamazepine, digoxin, phenobarbital, phenytoin, theophylline, tobramycin, vancomycin, and valproic acid were measured using leftover routine samples.
  
  
  RESULTS
  Good performance and comparability of the drug assays was seen on all systems for carbamazepine, phenytoin, and valproic acid except for phenytoin on the Dimension Vista. Deviations from the acceptance criteria were found with digoxin, phenobarbital, theophylline, tobramycin, and vancomycin. Despite a change of the analytical principle on the Roche systems for most drugs, the results demonstrated a very good between-system comparability of the concentration measured. Systematic deviations were found between AxSYM and ARCHITECT for digoxin, phenobarbital, and tobramycin, and between Dimension Xpand and Dimension Vista for digoxin and vancomycin.
  
  
  CONCLUSIONS
  The study revealed differences between assays, platforms, and assay principles. Care should be taken if methods or instruments are replaced in a laboratory. Laboratories are advised to perform their own method comparison studies and to inform their customers about the effect on the therapeutic ranges in case of observed clinically significant deviations.
authors.affiliation: *Central Institute of Clinical Chemistry and Laboratory Medicine, Klinikum Stuttgart, Stuttgart; †Department of Clinical Chemistry, University Medical Center Göttingen, Göttingen; and ‡Institute of Laboratory Medicine, Marienhospital Stuttgart, Stuttgart, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Shipkova
authors.forename: Darinka T
authors.initials: DT
authors.lastname: Petrova
authors.forename: Alexander E
authors.initials: AE
authors.lastname: Rosler
authors.forename: Matthias
authors.initials: M
authors.lastname: Orth
authors.forename: Jutta
authors.initials: J
authors.lastname: Engelmayer
authors.forename: Eberhard
authors.initials: E
authors.lastname: Wieland
authors.forename: Gunnar
authors.initials: G
authors.lastname: Brandhorst
authors.forename: Michael
authors.initials: M
authors.lastname: Oellerich
mesh_terms: D016903:Drug Monitoring / Q000379:methods*; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D004364:Pharmaceutical Preparations / Q000737:chemistry*
chemical_list: D004364:Pharmaceutical Preparations