title: Production and certification of four frozen human serum certified reference materials containing creatinine and electrolytes.
abstract: BACKGROUND
  This paper describes the preparation, analysis and certification of four frozen human serum certified reference materials (CRMs) containing creatinine and the electrolytes calcium, lithium, magnesium, potassium and sodium. These materials have been prepared to give concentrations of these analytes that cover the currently accepted analytical range.
  
  
  METHODS
  The analysis of the materials for certification purposes has been carried out using methodology traceable to primary standards, and which is acceptable as a reference method. The certification methods include liquid chromatography-mass spectrometry (LC-MS) with exact-matching isotope dilution calibration (EM-IDMS) for creatinine, inductively-coupled plasma optical emission spectroscopy (ICP-OES), ICP-MS and isotope-dilution inductively-coupled plasma mass spectroscopy (ID-ICP-MS) for the electrolytes.
  
  
  RESULTS
  The uncertainties estimated for these certified values include a component from the characterization measurements, as well as contributions from possible inhomogeneity and long-term instability. The certified values have been corroborated by measurements obtained in a major UK External Quality Assessment scheme, which have, with the exception of the determination of creatinine at a particularly low concentration, given excellent agreement.
  
  
  CONCLUSIONS
  The materials are intended for use by pathology laboratories and manufacturers of in vitro diagnostic (IVD) kits for validation of existing routine methodology to a traceable standard, which will promote harmonization between the different methods, instruments and IVD kits used in these laboratories.
authors.affiliation: Research and Technology Division, LGC Limited, Teddington TW11, 0LY, UK.
authors.forename: Romina P
authors.initials: RP
authors.lastname: Barbagallo
authors.forename: Nick
authors.initials: N
authors.lastname: Boley
authors.forename: Gill
authors.initials: G
authors.lastname: Holcombe
authors.forename: Sheila
authors.initials: S
authors.lastname: Merson
authors.forename: Chris
authors.initials: C
authors.lastname: Mussell
authors.forename: Caroline
authors.initials: C
authors.lastname: Pritchard
authors.forename: Peter
authors.initials: P
authors.lastname: Stokes
authors.forename: Steve
authors.initials: S
authors.lastname: Wood
authors.forename: David
authors.initials: D
authors.lastname: Ducroq
authors.forename: Annette
authors.initials: A
authors.lastname: Thomas
mesh_terms: D002138:Calibration; D002853:Chromatography, Liquid / Q000379:methods; D003404:Creatinine / Q000097:blood* / Q000592:standards*; D004573:Electrolytes / Q000097:blood* / Q000592:standards*; D006801:Humans; D013058:Mass Spectrometry / Q000379:methods; D012016:Reference Values
chemical_list: D004573:Electrolytes; D003404:Creatinine