Combined Association of the Fibrinogen-to-Albumin Ratio and the Uric Acid-to-Albumin Ratio with Mortality in Critically Ill Patients with Acute Kidney Injury Receiving Continuous Renal Replacement Therapy: A Retrospective Cohort Study

Background: The combined prognostic value of the fibrinogen-to-albumin ratio (FAR) and uric acid-to-albumin ratio (UAR) in acute kidney injury patients undergoing continuous renal replacement therapy remains unclear. Methods: This retrospective cohort study utilized the MIMIC-IV database. Adult patients with AKI receiving CRRT were included and stratified into four groups based on optimal FAR and UAR cut-offs. Multivariable Cox proportional hazards regression and restricted cubic spline analyses were employed to examine associations with 30-, 90-, and 360-day all-cause mortality. Results: Patients with high FAR/high UAR had the poorest survival (log-rank p < 0.001). After multivariable adjustment, high FAR/high UAR was associated with higher 30-day (HR = 2.17, 95%CI: 1.61–2.92) and 360-day mortality (HR = 1.50, 95%CI: 1.18–1.90) vs. low FAR/low UAR. The association was stronger in patients with an SOFA score > 12 or vasopressin use (interaction p < 0.05). Conclusions: In critically ill AKI patients undergoing CRRT, the combined assessment of the FAR and UAR is associated with elevated mortality risk. These readily obtainable composite markers may support risk stratification in clinical practice.