Association between serum calcium levels and in-hospital mortality in sepsis: A retrospective cohort study

Background: This study examines serum calcium levels and in-hospital mortality in patients with sepsis, a subject with contradictory findings in the existing literature. Methods: This retrospective cohort study utilized data from the MIMIC-IV database, focusing on adult patients diagnosed with sepsis between 2008 and 2019. The serum calcium levels were taken as the highest value within the first 24 h of Intensive Care Unit (ICU) admission. We performed Cox proportional hazards regression analyses in multivariable-adjusted models to investigate the association between serum calcium levels and in-hospital mortality. Restricted cubic spline functions were used to assess the nonlinear relationship, and threshold effect analysis was conducted to identify potential inflection points. Results: A total of 18,546 patients with sepsis were included in the study, and an in-hospital mortality rate of 16.9 % (3,126 out of 18,546) was obtained. Furthermore, a U-shaped relationship was observed between serum calcium concentrations and in-hospital mortality, with the lowest point at approximately 8.23 mg/dL. Hazard ratios were calculated as 0.75 (95 % CI: 0.67-0.85, P <0.001) on the left side and 1.10 (95 % CI: 1.04-1.16, P < 0.001) on the right side of the inflection point. Sensitivity analyses corroborated these results. Conclusion: The research identified a U-shaped correlation between serum calcium concentrations and in-hospital mortality rates among patients with sepsis, underscoring the importance of serum calcium monitoring in this patient population upon hospital admission.