Agreement of Electrolyte Measurements Between Arterial Blood Gas Analyzers and Central Laboratories in Critically Ill Patients with Acute Kidney Injury

Background: Electrolyte disturbances are common in critically ill patients with acute kidney injury (AKI) and often require urgent intervention. Arterial blood gas (ABG) analyzers provide rapid point-of-care electrolyte measurements, but their agreement with central laboratory analyzers in critically ill patients with AKI remains uncertain. This study evaluated the agreement between ABG and central laboratory measurements of sodium (Na+), potassium (K+), and chloride (Cl−). Methods: We conducted a retrospective observational study of adult critically ill patients with AKI admitted to a tertiary university hospital ICU between January 2013 and June 2024. Patients with paired electrolyte measurements obtained from an ABG analyzer (ABL800 Basic, Radiometer) and a central laboratory analyzer (Abbott Alinity) within 10 min were included. Agreement was assessed using Bland–Altman analysis and Passing–Bablok regression. Results: A total of 1870 critically ill patients with AKI were included. The mean bias (95% limits of agreement [LOA]) between ABG and central laboratory measurements was −0.68 mmol/L (−11.41 to 10.06) for sodium, −0.17 mmol/L (−1.46 to 1.12) for potassium, and 7.18 mmol/L (−4.15 to 18.51) for chloride. Potassium showed the narrowest LOA. Pearson correlation coefficients were 0.736, 0.642, and 0.728 for sodium, potassium, and chloride, respectively. Clinically meaningful discrepancies were observed in 7.0% of sodium, 14.1% of potassium, and 31.4% of chloride measurements. Conclusions: ABG-derived sodium and potassium measurements showed relatively good agreement with central laboratory measurements, particularly for potassium. However, clinically meaningful discrepancies occurred in a subset of measurements, suggesting that preanalytical factors and specimen quality may influence measurement reliability. ABG-derived electrolyte measurements may support rapid bedside assessment, whereas central laboratory measurements remain the reference standard.