title: A study to examine the accuracy of potassium measurements in clinical laboratories across Canada.
abstract: OBJECTIVE
  To assess the accuracy of potassium measurements in clinical laboratories across Canada.
  
  
  METHODS
  The flame atomic emission spectrophotometry reference method for the determination of potassium was established at the Canadian Reference Laboratory by using National Institute of Science and Technology standard reference materials. The method was subsequently used to assign target values for potassium to Canadian Reference Laboratory's External Quality Assessment human-serum-based testing material. A total of 503 laboratories participated and 9,279 individual External Quality Assessment test results were included in the study. Bias was determined by using difference plots.
  
  
  RESULTS
  Clinically significant bias (>1.6%) was observed in 45.9% of the laboratories. Bias ranged from 0.34 mmol/L to -0.54 mmol/L. At low concentrations (<3.5 mmol/L) a positive bias was most frequently observed (14.7% of analytical systems). At high potassium concentrations (>5.1 mmol/L) a negative bias was most frequently observed (31.4% of analytical systems).
  
  
  CONCLUSIONS
  Inaccuracy in potassium results can contribute to test redundancy and mismanagement of patients, while prohibiting the merger of laboratory data from disparate testing sites for the purpose of trending and consolidation within a "universal health record." Inaccurate test results and the lack of standardization among laboratories adversely impact our ability to establish common reference intervals and critical limits. This inability has an adverse effect on medical decisions and patient care.
authors.affiliation: Department of Pharmaceutical Sciences, University of Utrecht, Utrecht, The Netherlands.
authors.forename: M D
authors.initials: MD
authors.lastname: Haag
authors.forename: J R
authors.initials: JR
authors.lastname: Kelly
authors.forename: A
authors.initials: A
authors.lastname: Ho
authors.forename: D W
authors.initials: DW
authors.lastname: Seccombe
mesh_terms: D015982:Bias; D002138:Calibration; D002170:Canada; D019411:Clinical Laboratory Techniques / Q000379:methods* / Q000592:standards; D006801:Humans; D011188:Potassium / Q000097:blood*; D011786:Quality Control; D012016:Reference Values; D012044:Regression Analysis; D015203:Reproducibility of Results; D013054:Spectrophotometry, Atomic
chemical_list: D011188:Potassium