title: Recent trends in performance and current state of creatinine assays.
abstract: BACKGROUND
  Measured plasma or serum creatinine concentration is a primary component of equations used to calculate estimated glomerular filtration rate (eGFR). In recent years, most assay manufacturers have adopted creatinine calibration procedures that are traceable to the National Institute of Standards and Technology's Standard Reference Material 967.
  
  
  OBJECTIVE
  To examine the current performance of creatinine assays, to compare changes in assay performance since 2003, and to examine the reliability of laboratory eGFR calculations.
  
  
  METHODS
  Serum samples spiked with different concentrations of creatinine were analyzed by participating laboratories in the College of American Pathologists' LN24 survey. Participants' reported values were compared against values measured by liquid chromatography-isotope dilution mass spectrometry. Participants were asked to calculate the eGFR for certain samples, and results were compared with those obtained from the 4-parameter Modification of Diet in Renal Disease equation.
  
  
  RESULTS
  Biases among current creatinine methods are in the range of -5% to 10%, compared with -7% to 34% seen in a 2003 study. This degree of bias in eGFR calculations is of clinical significance only for concentrations near the cut points used to stage chronic kidney disease. Approximately 20% of laboratories report eGFR values that exceed ±1 mL/min per 1.73 m(2) from the expected eGFR using the 4-parameter Modification of Diet in Renal Disease equation.
  
  
  CONCLUSIONS
  Since 2003, there have been improvements in the performance of creatinine assays, which appear to be related to the adoption of standard reference materials for calibration. The effect of the observed method biases in clinical practice now appears minimal. Laboratories should continue to monitor the accuracy of eGFR calculations.
authors.affiliation: Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis 55455, USA. kille001@umn.edu
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Killeen
authors.forename: Edward R
authors.initials: ER
authors.lastname: Ashwood
authors.forename: Christina B
authors.initials: CB
authors.lastname: Ventura
authors.forename: Patricia
authors.initials: P
authors.lastname: Styer
mesh_terms: D003404:Creatinine / Q000097:blood*; D005919:Glomerular Filtration Rate; D006801:Humans; D007677:Kidney Function Tests / Q000295:instrumentation / Q000592:standards / Q000639:trends*; D007755:Laboratories, Hospital / Q000592:standards / Q000639:trends; D012016:Reference Values; D051436:Renal Insufficiency, Chronic / Q000097:blood* / Q000175:diagnosis; D015203:Reproducibility of Results
chemical_list: D003404:Creatinine