Determination of Electrolytes in Critical Illness Patients at Different pH Ranges: Whom Shall We Believe, the Blood Gas Analysis or the Laboratory Autoanalyzer?

Figure 2

Bland–Altman comparison of AA and ABG measurements for potassium and sodium. The plot of difference of 2 methods against the mean of 2 methods for potassium and sodium measurements, respectively. Bland–Altman plots are provided for total measurements showing the 95% limits of agreement. Comparison of AA and ABG for total potassium measurement results revealed that the limits of agreement were −0.241 to 0.391 mmol/L (a). These limits were clinically acceptable and the total ICC displayed a very good correlation of 0.949. In contrast, Bland–Altman comparison of the ABG and AA data for sodium revealed that the 95% limits of agreement were very wide (−5.99 to 6.59 mmol/L) for total measurements as well as in every pH subgroup, which was not clinically acceptable (b). Total ICC only reached a value of 0.830. Solid line: mean difference as well as maximum tolerated difference according to the US CLIA. Dashed lines: mean bias plus or minus standard deviation.

(a)

(b)