Publication:

Agreement between arterial and venous electrolyte levels in patients admitted to intensive care unit: a retrospective study

Background Electrolyte disturbances are common in critically ill patients and can significantly influence morbidity and mortality. Prompt detection is essential; however, serum electrolyte estimation using automated analyzers (AA) in central laboratories often suffers from delayed turnaround times. Point-of-care (POC) arterial blood gas (ABG) analyzers provide rapid results; however, their reliability compared to that of conventional autoanalyzers remains uncertain. This study aimed to evaluate the agreement between sodium and potassium levels measured in arterial and venous samples using the GEM 3500 (ABG) and Vitros 5600 (AA) analyzer, respectively.

Methods A retrospective study was conducted on 200 intensive care unit (ICU) patients in a secondary healthcare hospital between January and June 2024. The electrolytes were reported from both arterial and venous blood samples sent to the clinical biochemistry laboratory on the same day and at the same time. GEM 3500 and Vitros 5600 analyzers are used, respectively. Both methods use the direct ISE method. Statistical analyses included the Wilcoxon signed-rank test, Spearman’s correlation, and Bland-Altman plots to assess correlation and agreement.

Results The mean and standard deviation of sodium values (136.33±9.22 mmol/l in venous and 135.23±9.57 mmol/l in arterial blood) and potassium values (4.20±1.01 mmol/l and 4.01±0.97 mmol/l) were observed. The differences were statistically significant (p<0.001). Spearman’s correlation showed strong positive relationships (r=0.819 for sodium; r=0.844 for potassium, p<0.001). Bland-Altman analysis demonstrated that 97.5% of the sodium and 93.5% of the potassium values fell within the limits of agreement, suggesting good concordance.

Conclusions Sodium and potassium measurements obtained from arterial samples using the ABG analyzer can be used interchangeably with serum values derived from venous samples analyzed on an automated chemistry analyzer for the management of critically ill patients.