title: Relationship of the absolute difference between direct and indirect ion selective electrode measurement of serum sodium and the total protein concentration.
abstract: OBJECTIVE
  To derive the relationship for the difference between direct and indirect ion selective electrode measurements of serum sodium and the total protein concentration.
  
  
  METHODS
  Using modern analysers and independent specimens that covered the whole of the total protein range, linear relationships were derived for the difference between direct and indirect ion selective electrode measurements of serum sodium and the total protein concentration.
  
  
  RESULTS
  The regression data were as follows: absolute difference = 0.1196 TP - 5.9528, r(2) = 0.4555, p<10(-48); relative difference = 0.0849 TP - 4.1199, r(2) = 0.4153, p<10(-43).
  
  
  CONCLUSIONS
  A linear regression equation for the relationship of the absolute difference between direct and indirect ion selective electrode measurements of serum sodium and the total protein concentration can be validly derived. However, due to the large spread of data around the regression line, such equations should not be employed to decide when to use direct electrodes instead of indirect electrodes in routine clinical laboratories.
authors.affiliation: Department of Clinical Biochemistry, Ipswich Hospital, Ipswich, UK.
authors.forename: B J
authors.initials: BJ
authors.lastname: Jones
authors.forename: P J
authors.initials: PJ
authors.lastname: Twomey
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001798:Blood Proteins / Q000032:analysis*; D003951:Diagnostic Errors / Q000517:prevention & control; D006801:Humans; D017736:Ion-Selective Electrodes; D016014:Linear Models; D008875:Middle Aged; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012964:Sodium / Q000097:blood*
chemical_list: D001798:Blood Proteins; D012964:Sodium