Albumin-Anchored Composite Ratios of Blood Urea Nitrogen, C-Reactive Protein, Lactate, and Creatinine for Predicting Mortality in Chronically Ill Intensive Care Unit Patients

Background: This study aimed to evaluate the prognostic performance of four albumin-anchored ratios—blood urea nitrogen/albumin ratio (BAR), C-reactive protein/albumin ratio (CAR), lactate/albumin ratio (LAR), and albumin/creatinine ratio (ACR)—in predicting short-term mortality among intensive care unit (ICU) patients with pre-existing chronic comorbidities. Additionally, we assessed their incremental prognostic value beyond established severity scores such as APACHE II and SOFA. Materials and Methods: This retrospective cohort study included 520 chronically ill adult ICU patients admitted between July 2022 and July 2025. Patients with missing laboratory data, ICU stay <24 h, or postoperative monitoring only were excluded. BAR, CAR, LAR, and ACR were calculated from admission laboratory values. The primary outcome was 28-day mortality. Receiver operating characteristic (ROC) analyses, multivariate logistic regression, and model improvement metrics (C-statistics, NRI, IDI) were used to assess predictive performance. Results: Non-survivors had significantly higher BAR (15.0 vs. 8.2), CAR (39.2 vs. 19.1), and LAR (0.86 vs. 0.44) values and lower ACR (2.0 vs. 3.4) (all p < 0.001). In multivariate analysis, all four ratios independently predicted 28-day mortality (p < 0.001 for each). CAR showed the highest AUC (0.80), followed by LAR (0.79), BAR (0.78), and ACR (0.76). Incorporating all four ratios improved model discrimination (C-statistic 0.872 vs. 0.823; Δ = +0.049, p < 0.001) and reclassification (NRI = 0.162; IDI = 0.052). Conclusions: BAR, CAR, LAR, and ACR are independent and complementary predictors of short-term mortality in ICU patients with chronic comorbidities. Among them, CAR exhibited the best discriminative power. The combined use of these ratios enhanced risk prediction beyond traditional severity scores, suggesting their utility as simple, cost-effective markers for early mortality assessment. Because these indices are calculated from routinely measured laboratory parameters, they may represent practical and widely accessible tools for mortality risk stratification in routine ICU practice.