This retrospective cohort study investigated the relationship between the easily calculated Sodium–Chloride Difference (SCD) at the time of ICU admission and the patient’s subsequent 30-day mortality risk in 1,726 critically ill adults.

Using restricted cubic spline analysis, the researchers identified a significant non-linear association, with mortality risk sharply escalating at lower SCD values. Both spline modeling and ROC analysis consistently pinpointed 30 mmol/L as a critical threshold for prognostic significance.

The findings showed that patients admitted with an SCD less than 30 mmol/L (nearly 20% of the cohort) had a significantly and substantially higher 30-day mortality rate.

Crucially, this association remained robust and independent even after adjusting for major confounding factors like age, SOFA score, lactate levels, and comorbidities, with a significantly increased adjusted hazard ratio.

The study concludes that a low SCD at ICU admission serves as a valuable and readily available parameter for early risk stratification and may reflect key underlying physiological derangements involving the balance of sodium and chloride in critically ill patients.

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