Association of Urea-to-Creatinine Ratio with Functional Outcomes in Patients with Traumatic Brain Injury

Background: In patients with traumatic brain injury (TBI), proteins are considered the main source of energy. Previous studies have suggested that an increase in the urea-to-creatinine ratio (UCR) indicates the onset of protein catabolism. Therefore, we aimed to investigate the associations of the UCR with the functional independence measure (FIM). Methods: This single-center retrospective study included 291 patients aged 17–87 years who underwent inpatient rehabilitation within the first 6 months post-TBI. Their demographic, clinical, neuroradiological, and laboratory data (eGFR, urea, creatinine, UCR) were collected. Spearman’s correlation and hierarchical multivariate regression analyses adjusted for clinical covariates were performed. Results: The strongest significant positive correlation was found between the Glasgow Coma Scale (GCS) and FIM at admission (ρ = 0.488, p < 0.001) and between GCS and FIM at discharge (ρ = 0.340, p < 0.001). A significant negative correlation was found between the discharge UCR and FIM at discharge (ρ = −0.262, p < 0.003), as well as with the change in FIM (ρ = −0.207, p < 0.02). Patients with UCRs ≥ 80 had a significantly lower discharge FIM compared to patients with UCRs < 80 (median 27 vs. 40; p = 0.02). The significant independent predictors of discharge FIM were the nutritional route (NGT/PEG), level of consciousness, and FIM at admission. The UCR did not remain independently associated with the discharge FIM (ΔR2 = 0.004, Cohen’s f2 = 0.014). Conclusions: Although UCR is associated with functional outcomes measured by FIM in TBI patients, it is not an independent predictor of these outcomes but rather a biomarker of catabolic burden.