title: Commutability limitations influence quality control results with different reagent lots.
abstract: BACKGROUND
  Good laboratory practice includes verifying that each new lot of reagents is suitable for use before it is put into service. Noncommutability of quality control (QC) samples with clinical patient samples may preclude their use to verify consistency of results for patient samples between different reagent lots.
  
  
  METHODS
  Patient sample results and QC data were obtained from reagent lot change verification records for 18 QC materials, 661 reagent lot changes, 1483 reagent lot change-QC events, 82 analytes, and 7 instrument platforms. The significance of between-lot differences in the results for QC samples compared with those for patient samples was assessed by a modified 2-sample t test adjusted for heterogeneity of QC and patient sample measurement variances.
  
  
  RESULTS
  Overall, 40.9% of reagent lot change-QC events had a significant difference (P < 0.05) between results for QC samples compared with results for patient samples between 2 reagent lots. For QC results with differences <1.0 SD interval (83.1% of total), 37.7% were significantly different from the changes observed for patient samples. For QC results with differences ≥1.0 SD interval (16.9% of total), 57.0% were significantly different from those for patient samples.
  
  
  CONCLUSIONS
  Occurrence of noncommutable results for QC materials was frequent enough that the QC results could not be used to verify consistency of results for patient samples when changing lots of reagents.
authors.affiliation: Department of Pathology, Virginia Commonwealth University, Richmond, VA, USA. gmiller@vcu.edu
authors.forename: W Greg
authors.initials: WG
authors.lastname: Miller
authors.forename: Aybala
authors.initials: A
authors.lastname: Erek
authors.forename: Tina D
authors.initials: TD
authors.lastname: Cunningham
authors.forename: Olajumoke
authors.initials: O
authors.lastname: Oladipo
authors.forename: Mitchell G
authors.initials: MG
authors.lastname: Scott
authors.forename: Robert E
authors.initials: RE
authors.lastname: Johnson
mesh_terms: D019963:Clinical Chemistry Tests / Q000592:standards* / Q000706:statistics & numerical data; D003627:Data Interpretation, Statistical; D006801:Humans; D007202:Indicators and Reagents / Q000592:standards*; D011786:Quality Control; D011933:Reagent Kits, Diagnostic / Q000592:standards*; D012015:Reference Standards; D015203:Reproducibility of Results
chemical_list: D007202:Indicators and Reagents; D011933:Reagent Kits, Diagnostic