Comparison of different methods for measurement of electrolytes in patients admitted to the intensive care unit

OBJECTIVES To investigate whether electrolyte levels measured by using blood gas analyzers (ABG) and auto-analyzers (AA) are equivalent and can be used interchangeably. METHODS This observational prospective study was conducted in 100 patients admitted to the Intensive Care Unit, Adnan Menderes University School of Medicine, Aydin, Turkey, between March and August 2014. Samples for both AA and ABG analyzers were collected simultaneously from invasive arterial catheters of patients. The electrolyte levels were measured by using 2 methods. RESULTS The mean sodium level measured by ABG was 136.1 ± 6.3 mmol/L and 137.8 ± 5.4 mmol/L for AA (p=0.001). The Pearson's correlation coefficient was 0.561 (p less than 0.001). The Bland-Altman 95% limits of agreement were -9.4 to 12.6 mmol/L. The mean potassium levels measured by ABG was 3.4 ± 0.7 mmol/L and AA was 3.8 ± 0.7 mmol/L (p=0.001). The Bland-Altman comparison limits were -0.58 to 1.24 and the associated Pearson's correlation coefficient was 0.812 (p less than 0.001). CONCLUSION The results of the 2 analyzing methods, in terms of sodium, were not equivalent and could not be used interchangeably. However, according to the statistical analyses results, by including, but not blindly trusting these findings, urgent and vital decisions could be made by the potassium levels obtained from the BGA, but a simultaneous follow-up sample had to be sent to the central laboratory for confirmation.