Dysnatremia is a common electrolyte disturbance among critically ill patients and may have important prognostic implications in the context of sepsis. This study aims to investigate the independent association between admission serum sodium abnormalities and 30-day mortality in patients with sepsis, and to evaluate the mortality risk across the full spectrum of sodium levels at emergency department (ED) presentation.

This retrospective cohort study included adult patients diagnosed with sepsis in the ED of a tertiary care hospital between January 1, 2022, and January 1, 2025. Dysnatremia was defined as serum sodium <135 or > 145 mmol/L at admission. The primary outcome was 30-day all-cause mortality. Multivariate logistic regression and generalized additive modeling (GAM) were used to evaluate the association between serum sodium and mortality, adjusting for relevant clinical and laboratory covariates.

A total of 793 patients were included in the final analysis. The overall 30-day mortality rate was 23.0 %. Dysnatremia was independently associated with increased risk of 30-day mortality (adjusted OR: 4.06, 95 % CI: 1.67–10.19, p  = 0.002). Additional predictors included elevated lactate, hsCRP, procalcitonin, and SOFA scores. The association between serum sodium and mortality exhibited a non-linear pattern, with both hypo- and hypernatremic extremes showing higher mortality compared to the normonatremic range. The GAM model demonstrated strong discriminative performance (ROC-AUC: 0.893).

Abnormal serum sodium levels at presentation were independently associated with short-term mortality in patients with sepsis. These findings support the inclusion of sodium measurements in early clinical assessment and risk stratification of septic patients in the ED.