To investigate the relationship between serum albumin (ALB) levels on the first day of intensive care unit (ICU) admission and in-hospital mortality risk in patients with sepsis complicated by chronic heart failure (CHF), and to evaluate for a potential non-linear association.

This was a retrospective cohort study using data from the medical information mart for intensive care Ⅳ (MIMIC-Ⅳ) database. The patients with sepsis and CHF who met the study criteria were included. Demographic data, such as age and gender, as well as disease severity scores (simplified acute physiology score Ⅱ, sequential organ failure assessment), vital signs (e.g., body temperature, heart rate), laboratory indicators (e.g., serum albumin, white blood cell count), and comorbidities (e.g., hypertension, diabetes) were collected. Multivariable Logistic regression analysis was used to assess the independent association between ALB and in-hospital mortality. Generalized additive models and two-piecewise regression models were employed to analyze the non-linear relationship between ALB and in-hospital mortality risk and to identify the inflection point.

A total of 1 093 patients with sepsis complicated by CHF were included. The mean age was (74.2±12.5) years, and 57.5% (628/1 093) were male. The in-hospital mortality rate was 25.3% (276/1 093). After adjusting for confounding factors using multivariable Logistic regression, for every 1 g/L increase in ALB, the in-hospital mortality risk decreased by 5% (OR = 0.95, 95%CI 0.92-0.98, P = 0.002). Smooth curve fitting and two-piecewise regression analysis further revealed a significant non-linear relationship between ALB and in-hospital mortality risk, with an inflection point at 28 g/L. Specifically, when ALB levels were below 28 g/L, every 1 g/L increase in ALB was associated with a 12% reduction in mortality risk (OR = 0.88, 95%CI 0.83-0.95, P < 0.001). However, when ALB levels were above 28 g/L, ALB had no statistically significant impact on mortality risk (OR = 1.01, 95%CI 0.95-1.07, P = 0.826).

Low ALB levels on the first day of ICU admission in patients with sepsis complicated by CHF are independently associated with an increased risk of in-hospital mortality, and there is a non-linear relationship between them. When ALB levels are below 28 g/L, higher ALB levels have a significant protective effect on reducing in-hospital mortality.