The Association Between C-Reactive Protein-to-Albumin Ratio and in-Hospital Mortality in Patients with Klebsiella pneumoniae Bloodstream Infection: A Retrospective Cohort Study

Background: The C-reactive protein-to-albumin ratio (CAR), integrating inflammation (CRP) and physiological reserve (albumin), shows promise as a prognostic biomarker in critical illness, but its specific role in Klebsiella pneumoniae bloodstream infection (KP-BSI) mortality has not been confirmed. Methods: Between 2019 and 2024, 264 adult patients with KP-BSI at a tertiary medical center were included in this retrospective cohort study. The primary endpoint was in-hospital mortality, Patients were categorized into three groups according to tertiles of the CAR: T1 6.91. To assess the relationship between serum CAR levels and mortality risk, we applied multivariable Cox proportional hazards models and constructed Kaplan–Meier survival curves, with subgroup analyses incorporating interaction testing across sex, age, diabetes, septic shock, and CRKP status, as well as sensitivity analyses excluding patients with chronic liver disease, those with missing covariates, and including those with a length of hospital stay exceeding 180 days. The discriminatory performance of CAR was further assessed using receiver operating characteristic (ROC) curve analysis. Results: Among the 264 patients included in the final analysis, 121 (45.8%) died during hospitalization. Non-survivors showed significantly higher CAR (7.1 ± 3.4) than survivors (4.8 ± 3.0) (p< 0.001). After adjusting for potential confounders, each unit increase in CAR was independently associated with a higher risk of in-hospital mortality (hazard ratio (HR)=1.12, 95% confidence interval (CI): 1.07– 1.19, p< 0.001). When treated as a categorical variable, compared to the reference group (T1 group), patients in the highest tertile (T3) had a substantially elevated mortality risk (HR=3.12, 95% CI: 1.83– 5.34, P< 0.001). Subgroup analyses and sensitivity analyses consistently supported the robustness of the results. The ROC analysis demonstrated that CAR had moderate discriminatory ability. Conclusion: CAR is independently associated with in-hospital mortality in patients with KP-BSI. This readily available biomarker offers meaningful early risk stratification and may help identify patients at elevated risk who could benefit from closer monitoring and targeted clinical intervention. Keywords: Klebsiella pneumoniae , bloodstream infection, C-reactive protein, albumin, CAR