title: Two evaluation budgets for the measurement uncertainty of glucose in clinical chemistry.
abstract: BACKGROUND
  Measurement uncertainty characterizes the dispersion of the quantity values attributed to a measurand. Although this concept was introduced to medical laboratories some years ago, not all medical researchers are familiar with it. Therefore, the evaluation and expression of measurement uncertainty must be highlighted using a practical example.
  
  
  METHODS
  In accordance with the procedure for evaluating and expressing uncertainty, provided by the Joint Committee for Guides in Metrology (JCGM), we used plasma glucose (Glu) as an example and defined it as the measurand. We then analyzed the main sources of uncertainty, evaluated each component of uncertainty, and calculated the combined uncertainty and expanded uncertainty with 2 budgets for single measurements and continuous monitoring, respectively.
  
  
  RESULTS
  During the measurement of Glu, the main sources of uncertainty included imprecision, within-subject biological variance (BV(w)), calibrator uncertainty, and systematic bias. We evaluated the uncertainty of each component to be 1.26%, 1.91%, 5.70%, 0.42%, and -2.87% for within-run imprecision, between-day imprecision, BV(w), calibrator uncertainty, and systematic bias, respectively. For a single specimen, the expanded uncertainty was 7.38% or 6.1±0.45 mmol/L (κ=2); in continuous monitoring of Glu, the expanded uncertainty was 13.58% or 6.1±0.83 mmol/L (κ=2).
  
  
  CONCLUSIONS
  We have demonstrated the overall procedure for evaluating and reporting uncertainty with 2 different budgets. The uncertainty is not only related to the medical laboratory in which the measurement is undertaken, but is also associated with the calibrator uncertainty and the biological variation of the subject. Therefore, it is helpful in explaining the accuracy of test results.
authors.affiliation: Clinical Laboratories, The First Affiliated Hospital of Chongqing Medical University, China. chenhui789@gmail.com
authors.forename: Hui
authors.initials: H
authors.lastname: Chen
authors.forename: Ling
authors.initials: L
authors.lastname: Zhang
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Bi
authors.forename: Xiaoling
authors.initials: X
authors.lastname: Deng
mesh_terms: D001774:Blood Chemical Analysis / Q000379:methods / Q000592:standards; D019963:Clinical Chemistry Tests / Q000379:methods* / Q000592:standards; D005947:Glucose / Q000032:analysis* / Q000592:standards; D006801:Humans; D015233:Models, Statistical; D011786:Quality Control; D035501:Uncertainty
chemical_list: D005947:Glucose