Relationship between the creatinine/albumin ratio and the ICU mortality rate of patients with acute respiratory distress syndrome: A retrospective cohort study

Background : Creatinine (Cr) and albumin (ALB) are widely recognized as predictive biomarkers of mortality across various disease conditions, including patients with acute respiratory distress syndrome (ARDS). Nevertheless, limited evidence is available regarding the associations between the creatinine-to-albumin ratio and clinical outcomes in ARDS patients. This study aimed to assess the prognostic value of the creatinine-to-albumin ratio in predicting 28-day mortality, all-cause mortality, and the incidence of acute kidney injury (AKI) among patients diagnosed with ARDS. Methods : This retrospective cohort study utilized clinical data extracted from the database of Beth Israel Deaconess Medical Center (BIDMC) in Boston, Massachusetts, USA, spanning the period from 2008--2019. The creatinine‒albumin ratio (CAR) was calculated on the basis of measurements taken within 24 hours of patient admission. Kaplan‒Meier (K‒M) analysis was employed to compare 28-day mortality, all-cause mortality, and the incidence of acute kidney injury across the four patient groups. A Cox proportional hazards regression model and RCS were used to assess the relationships between the CAR and the risks of 28-day mortality, long-term all-cause mortality, and acute kidney injury. The predictive performance of the CAR—including its sensitivity, specificity, and AUC—was evaluated via receiver operating characteristic (ROC) curve analysis for the aforementioned outcomes in patients with ARDS. Subgroup analyses were also conducted to further validate the robustness and reliability of our findings. Results : A total of 1,233 patients were enrolled in the study. K‒M analysis revealed statistically significant differences in 28-day mortality, overall all-cause mortality, and the incidence of AKI across CAR quartiles (log-rank P < 0.001). Patients with elevated CAR levels presented increased risks of both 28-day and all-cause mortality, as well as a higher cumulative incidence of AKI. After adjusting for potential confounding factors, the multivariate Cox proportional hazards regression model confirmed a statistically significant association between the CAR and each of the three clinical outcomes. Furthermore, RCS analysis demonstrated a significant U-shaped nonlinear relationship between the CAR and these outcomes. ROC curve analysis revealed that the AUC values for the continuous CAR in predicting 28-day mortality, all-cause mortality, and AKI in patients with ARDS were 0.729, 0.716, and 0.785, respectively. When analyzed by quartiles, the corresponding AUCs were slightly improved at 0.732, 0.719, and 0.794. Subgroup analyses indicated that the associations between the CAR and clinical outcomes were more pronounced among patients aged >65 years, males, and those with a history of myocardial infarction or peripheral vascular disease. Notably, in patients with cerebrovascular disease, the risk of mortality did not increase with increasing CAR (hazard ratio [HR] = 0.88, P = 0.414), and the risk of AKI was attenuated in patients with diabetes and chronic complications (HR = 0.79, P = 0.303). Conclusion: The CAR can serve as an independent predictor of 28-day mortality, all-cause mortality, and acute kidney injury. This study also revealed differences in the CAR among different subgroups, which may provide promising prognostic biomarkers for risk stratification and clinical management of patients with ARDS.