title: Measuring zinc on the Roche cobas c502 analyzer-Validation, comparison, and pre-analytic aspects.
abstract: OBJECTIVE
  Characterization of an in vitro diagnostic zinc assay (LT-SYS) on a Roche cobas c502 analyzer and evaluation of the influence of pre-analytic factors on zinc concentration measurements.
  
  
  METHODS
  Imprecision, bias, linearity, limit of blank (LoB), and limit of detection (LoD) were established and method comparisons were performed based on the respective CLSI guidelines. The influence of time elapsed until analysis, the usage of a pneumatic tube delivery system (PTDS) and of special trace element sample tubes was evaluated as well.
  
  
  RESULTS
  Estimates of imprecision ranged from 0.9% to 5.0% and bias was low with 1.3% and 1.5% deviation from target value. Linearity was met for the measuring range of 1.15-34.7 μmol/L (7.51-226.9 μg/dL), LoB and LoD were 0.17 μmol/L (1.11 μg/dL) and 0.73 μmol/L (4.77 μg/dL) respectively. The method comparison revealed an average deviation of 8.44% (y=0.542+1.036x). Plasma samples had 7.3% higher zinc values than serum samples on the average. Zinc values of uncentrifuged serum and plasma samples increased 20% in 8 hours, while after centrifugation no significant increase could be detected. Usage of PTDS increased zinc values by 17% and usage of trace element sample tubes showed no advantage over normal ones.
  
  
  CONCLUSIONS
  The LT-SYS zinc assay showed a fully acceptable performance with good degrees of imprecision and bias, no deviation from linearity and both a very low LoB and LoD. Samples for zinc analysis should be centrifuged timely and transport over PTDS should be avoided.
authors.affiliation: Zentrallabor, Department of Laboratory Medicine, University Hospital Halle, Halle (Saale), Germany.|Department of Biology, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany.
authors.forename: Frank Bernhard
authors.identifier: http://orcid.org/0000-0003-4354-9952
authors.initials: FB
authors.lastname: Kraus
authors.affiliation: Zentrallabor, Department of Laboratory Medicine, University Hospital Halle, Halle (Saale), Germany.
authors.forename: Beatrice
authors.identifier: http://orcid.org/0000-0003-2660-4921
authors.initials: B
authors.lastname: Ludwig-Kraus
mesh_terms: D001774:Blood Chemical Analysis / Q000379:methods* / Q000592:standards*; D006801:Humans; D057230:Limit of Detection; D016014:Linear Models; D015203:Reproducibility of Results; D015032:Zinc / Q000097:blood*
chemical_list: D015032:Zinc
keywords: Roche cobas c502; clinical chemistry; method comparison; method validation; zinc