Association between serum calcium levels and mortality in critically ill patients with gastrointestinal bleeding: a retrospective cohort study.

BACKGROUND: The prognostic value of serum total calcium levels in critically ill patients with gastrointestinal bleeding remains unclear. This study aimed to investigate the association between baseline serum total calcium levels and mortality in critically ill patients with gastrointestinal bleeding using the electronic Intensive Care Unit (eICU) database. METHODS: This retrospective cohort study was based on data collected from the eICU Collaborative Research Database in 2014 and 2015. Critically ill patients with gastrointestinal bleeding were included in this study. The exposure variable was the baseline serum calcium level. The primary outcome was hospital mortality, and the secondary outcome was intensive care unit (ICU) mortality. The non-linear relationship between serum calcium levels and mortality was determined using a generalised additive model and smooth curve fitting, and we calculated the inflection point. RESULTS: A total of 10 731 eligible patients were included. The hospital mortality and ICU mortality rates were 10.49% and 6.53% respectively. After adjusting for potential confounding factors, a U-shaped relationship was detected between serum calcium levels and mortality. The first inflection point was 8.5 mg/dL, and the second inflection point was 10.3 mg/dL. On the left side of the first inflection point (serum calcium <8.5 mg/dL), serum calcium levels were negatively associated with both hospital mortality (OR = 0.85, 95% CI 0.76-0.95) and ICU mortality (OR = 0.82, 95% CI 0.72-0.93). Conversely, on the right side of the second inflection point (serum calcium >10.3 mg/dL), serum calcium levels were positively associated with both hospital mortality (OR = 1.57, 95% CI 1.05-2.34) and ICU mortality (OR = 1.56, 95% CI 1.02-2.38). CONCLUSIONS: A U-shaped relationship between serum total calcium levels and mortality was observed in critically ill patients with gastrointestinal bleeding. Serum total calcium levels were associated with mortality in such patients, and this association has potential reference significance for risk assessment.