title: Results of the recalibration of creatinine measurement with  the modular Beckman Coulter Jaffe creatinine method.
abstract: BACKGROUND
  Serum creatinine is important for detecting the beginning of a decline in kidney function. The Beckman Coulter Jaffe reagents for measuring creatinine have been standardized to the internationally accepted reference method: isotope dilution mass spectrometry (IDMS). The impact of this recalibration on the Beckman Coulter modular or cup (stat) Jaffe method is studied.
  
  
  METHODS
  Recalibrated Jaffe (calibrator set points IDMS traceable) and classic National Institute of Standards and Technology (NIST) creatinine methods (traceable to NIST 914a) were compared with an enzymatic method (Sentinel, traceable to NIST SRM 967). All measurements were performed on Synchron DxC 800 systems. Imprecision of the routine methods was studied using the Clinical and Laboratory Standards Institute (CLSI) protocols and laboratory quality survey. Thirteen plasma pools, with concentrations < 354 mmol/L, were analyzed with a gas chromatography isotope dilution mass spectrometry (GC-IDMS) method and routine methods. Total error of 8.2% based on biological variability, set on the GC-IDMS values and acceptance criteria (bias < 5%, imprecision < 8% at concentrations ≥ 88.4 mmol/L and a maximum 10% increase in the relative error of estimated glomerular filtration rate (eGFR) of the National Kidney Disease Educational Program (NKDEP) were used for evaluating analytical performance of the routine methods studied.
  
  
  RESULTS
  After recalibration of the Jaffe method, median bias (mmol/L) decreased from 12.4 (95% CI: 9.1-21.2) to 7.3 (95% CI: 1.5-10.5). Imprecision of the Jaffe method is in agreement with the claim of the manufacturer, namely < 9 mmol/L or < 3% below or above 292 mmol/L. Below creatinine of 88.4 mmol/L, imprecision of the recalibrated Jaffe and enzymatic methods is between 4.1% and 6.9%, and 5.0% and 7.1%, respectively, and significantly different (p = 0.02 for both the Jaffe and enzymatic methods) from the goal, based on biological variability, of 2.7%. For the adult pools, all recalibrated Jaffe and enzymatic results fall within the total error of 8.2%. In the pediatric samples, one-third of the recalibrated Jaffe and three of the six enzymatic results fall within this total error goal.
  
  
  CONCLUSIONS
  Recalibration significantly reduced bias of the Jaffe method. For pediatric samples, recalibrated Jaffe results do not comply with either the imprecision goal or the total error based on biological variability. Adult recalibrated Jaffe results are in compliance with the goals based on biological variability and with the acceptance criteria from the NKDEP.
authors.affiliation: Université Catholique de Louvain, Cliniques Universitaires Saint-Luc, Brussels, Belgium.
authors.forename: Catherine
authors.initials: C
authors.lastname: Fillée
authors.forename: Guido
authors.initials: G
authors.lastname: Vranken
authors.forename: Myriam
authors.initials: M
authors.lastname: Othmane
authors.forename: Marianne
authors.initials: M
authors.lastname: Philippe
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Allaeys
authors.forename: Anne
authors.initials: A
authors.lastname: Courbe
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Ruelle
authors.forename: Rudy
authors.initials: R
authors.lastname: Peeters
mesh_terms: D000328:Adult; D001774:Blood Chemical Analysis / Q000379:methods*; D002138:Calibration; D003404:Creatinine / Q000097:blood* / Q000592:standards; D008401:Gas Chromatography-Mass Spectrometry / Q000592:standards; D005919:Glomerular Filtration Rate; D006801:Humans; D007201:Indicator Dilution Techniques; D011933:Reagent Kits, Diagnostic; D012044:Regression Analysis
chemical_list: D011933:Reagent Kits, Diagnostic; D003404:Creatinine