Nonlinear Association between AST/ALT Ratio and 28-Day Mortality in Critically Ill Cirrhotic Patients: A Retrospective Cohort Study

Background The aspartate aminotransferase-to-alanine aminotransferase (AST/ALT) ratio is a biochemical marker that has been demonstrated in recent years to be significantly linked to unfavorable clinical outcomes across different patient populations. However, the function of this ratio in patients with severe cirrhosis remains to be elucidated. This study aimed to examine the link between the AST/ALT ratio and mortality among cirrhosis patients in the intensive care unit. Methods This retrospective cohort analysis utilized the MIMIC-IV database to study 2,090 liver cirrhosis patients with their first ICU admission between 2008 and 2019. The AST/ALT ratio, assessed within the initial 24 hours of ICU admission, served as the exposure variable. The primary outcome measure was ICU mortality at 28 days. A multivariate linear regression model was used to assess the relationship between the AST/ALT ratio and 28-day ICU mortality. Potential nonlinear relationships were examined through the use of smooth curve fitting techniques and saturation effect analyses. Furthermore, stratified analyses and interaction testing were conducted, with participants categorized according to demographic variables and clinical characteristics. Results The present study comprised 2,990 patients suffering from liver cirrhosis and classified as being in critical condition. The patients had a mean age of 59.1 years, with 65.0% being male, and an ICU mortality rate of 29.0%. After multivariate adjustment, the AST/ALT ratio was independently associated with 28-day ICU mortality in cirrhotic patients (OR = 1.1, 95% CI 1.0–1.2; p = 0.015). A nonlinear relationship was observed, with an inflection point at 3.6. Below this threshold, each unit increase was linked to a 40% higher mortality risk (OR = 1.4, 95% CI 1.2–1.6, p < 0.001), while the association leveled off beyond this point (OR = 1.0, 95% CI 0.8–1.1, p = 0.600). Subgroup analyses and interaction tests confirmed the consistent association between the AST/ALT ratio and 28-day ICU mortality, with all interaction P values exceeding 0.05. Conclusions The AST/ALT ratio independently predicts 28-day mortality in critically ill cirrhotic patients, exhibiting a non-linear association with short-term mortality. This discovery could enhance risk assessment in the ICU and inform clinical decisions.