Correlation and Agreement Between Blood Gas vs Central Laboratory Electrolyte Measurements in Critically Ill Children

INTRODUCTION: Electrolyte monitoring is essential in pediatric intensive care units (PICUs), where rapid clinical decisions are frequently required. Blood gas analyzers (BGAs) provide fast, bedside results; however, their agreement with central laboratory analyzers (CLAs) remains a matter of debate, particularly in pediatric populations. To evaluate the correlation, agreement, and clinical interchangeability between electrolyte measurements obtained from a BGA and a CLA in pediatric intensive care patients.
METHODS: In this retrospective study, PICU patients with simultaneous BGA and CLA electrolyte measurements were included. Sodium, potassium, and chloride values obtained from the two methods were compared. Correlation analysis was performed using Spearman’s test, and agreement was assessed using Bland–Altman analysis. Predefined clinical acceptability limits were applied. Subgroup analysis was conducted based on acid–base status.
RESULTS: A total of 1,923 paired measurements were analyzed. Significant correlations were observed between BGA and CLA for sodium (ρ=0.656), potassium (ρ=0.794), and chloride (ρ=0.714) (all p<0.001). However, Bland–Altman analysis demonstrated wide limits of agreement for all parameters, with a substantial proportion of measurements falling outside predefined clinical acceptability limits. Subgroup analysis showed slightly stronger correlations in patients with acidosis, whereas sodium correlation was lower in the alkalosis group. Despite these variations, limits of agreement remained similar across acid–base subgroups.
DISCUSSION AND CONCLUSION: Although BGA electrolyte measurements show significant correlation with central laboratory results, the wide limits of agreement indicate that the two methods are not reliably interchangeable in clinical practice. While BGA provides rapid and clinically valuable information, confirmation with central laboratory measurements is recommended, particularly before making critical treatment decisions.

Keywords: Blood gas analysis, electrolytes, pediatric intensive care unit, point-of-care testing