title: A mechanism-based way to evaluate commutability of control materials for enzymatic measurements. The example of gamma-glutamyltransferase.
abstract: BACKGROUND
  Commutability is an essential requirement for control materials used in external quality assessment schemes. Testing control materials for commutability requires costly and time-consuming experiments. The aim of our work was the validation of a more effective way to evaluate commutability.
  
  
  METHODS
  Commutability of two control materials for gamma-glutamyltransferase (GGT) activity between IFCC reference method and four routine methods (Abbott, IL, Roche, Siemens) was tested with the conventional approach and with a new one. The new approach consisted in assessing the effects on the two controls and on two human serum pools, of similar GGT concentrations, of modifications of the measurement conditions (pH, substrate and buffer concentration). The effects of these variations on the two types of materials were compared.
  
  
  RESULTS
  Low GGT activity control was commutable in all method comparisons, the high level control was non-commutable for Abbott and Roche. Both controls showed behavior different from human pools when changing the measurement conditions, but this fact had significant effects only for the conditions of Abbott and Roche methods, confirming the results of the conventional approach.
  
  
  CONCLUSIONS
  The proposed approach seems able to identify the reasons for non-commutability and to anticipate the final commutable or non-commutable behavior of the material.
authors.affiliation: Diagnostica e Ricerca San Raffaele, Istituto Scientifico Universitario San Raffaele, Milano, Italy. Electronic address: carobene.anna@hsr.it.
authors.forename: Anna
authors.initials: A
authors.lastname: Carobene
authors.forename: Elena
authors.initials: E
authors.lastname: Guerra
authors.forename: Ferruccio
authors.initials: F
authors.lastname: Ceriotti
mesh_terms: D002021:Buffers; D057075:Enzyme Assays / Q000592:standards*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015588:Observer Variation; D011786:Quality Control; D012015:Reference Standards; D015203:Reproducibility of Results; D013379:Substrate Specificity; D005723:gamma-Glutamyltransferase / Q000097:blood* / Q000592:standards
chemical_list: D002021:Buffers; D005723:gamma-Glutamyltransferase
keywords: CLSI; Clinical and Laboratory Standards Institute; Commutability; Control materials; EQAS; GGT; Gamma-glutamyltransferase; Gly-Gly; IFCC; IL; Instrumentation Laboratory; International Federation of Clinical Chemistry and Laboratory Medicine; International Vocabulary of Metrology; Lyo 1; Lyo 2; PI; Pool A; Pool N; Reference measurement procedure; VIM; external quality assessment scheme; gamma-glutamyltransferase; glycylglycine; lyophilized material level 1; lyophilized material level 2; pool abnormal; pool normal; two-tailed 95% prediction interval