The reproducibility of Stewart parameters for acid-base diagnosis using two central laboratory analyzers.
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..
Nguyen
Ba-Vinh
BV
Department of Anesthesiology and Critical Care,Clermont Tonnerre Military Hospital, Brest, France. bavinh@free.fr
Vincent
Jean-Louis
JL
Hamm
Jean Baptiste
JB
Abalain
Jean-Hervé
JH
Carre
Jean-Luc
JL
Nowak
Emmanuel
E
Ahmed
Mehdi Ould
MO
Arvieux
Charles C
CC
Gueret
Gildas
G
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
D015415:Biomarkers