title: The reproducibility of Stewart parameters for acid-base diagnosis using two central laboratory analyzers.
abstract: BACKGROUND
  Acid-base derangements can be interpreted using the Stewart-Fencl approach, which includes calculation of the apparent strong ion difference (SID(app)), the effective SID (SID(eff)), and the strong ion gap (SIG). These calculations require the measurement of several variables. We hypothesized that the SID and SIG calculated by different analyzers would not be reproducible because of variability in the measured values.
  
  
  METHODS
  In this prospective observational study conducted in a biochemistry laboratory, we analyzed 179 routine blood samples from consecutive patients over a 3-mo period using two automated blood chemistry analyzers, the LX20 (Beckman) and the Modular (Roche). Measured and calculated parameters from the two analyzers were compared.
  
  
  RESULTS
  Although the correlation between measured values was satisfactory, there were large differences in the limits of agreement for calculated values (SID(app): 9.6 mEq/L, SID(eff): 6.4 mEq/L, and SIG: 11.7 mEq/L) and a weak correlation (SID(app): r(2) = 0.54 and SIG: r(2) = 0.12) between the analyzers.
  
  
  CONCLUSIONS
  The results of the Stewart-Fencl approach for interpretation of acid-base status can vary according to the analyzer used. These differences may have important clinical and research implications..
authors.affiliation: Department of Anesthesiology and Critical Care,Clermont Tonnerre Military Hospital, Brest, France. bavinh@free.fr
authors.forename: Ba-Vinh
authors.initials: BV
authors.lastname: Nguyen
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Vincent
authors.forename: Jean Baptiste
authors.initials: JB
authors.lastname: Hamm
authors.forename: Jean-Hervé
authors.initials: JH
authors.lastname: Abalain
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Carre
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Nowak
authors.forename: Mehdi Ould
authors.initials: MO
authors.lastname: Ahmed
authors.forename: Charles C
authors.initials: CC
authors.lastname: Arvieux
authors.forename: Gildas
authors.initials: G
authors.lastname: Gueret
mesh_terms: D000136:Acid-Base Equilibrium; D000137:Acid-Base Imbalance / Q000097:blood / Q000175:diagnosis*; D015415:Biomarkers / Q000097:blood; D001774:Blood Chemical Analysis / Q000295:instrumentation*; D004867:Equipment Design; D006801:Humans; D016014:Linear Models; D008954:Models, Biological; D015588:Observer Variation; D011237:Predictive Value of Tests; D011446:Prospective Studies; D015203:Reproducibility of Results
chemical_list: D015415:Biomarkers