Glucose-to-potassium ratio has a non-linear J-shaped association with acute kidney injury risk in traumatic brain injury

Acute kidney injury (AKI) is a severe complication of traumatic brain injury (TBI) associated with poor prognosis. The glucose-to-potassium ratio (GPR), an emerging marker of metabolic stress, may play a role in post-TBI AKI, but its precise relationship is unclear. This retrospective cohort study investigated the association between early-admission GPR and AKI in 2,388 TBI patients from the MIMIC-IV database. Using multivariable logistic regression and restricted cubic spline (RCS) models, we explored both linear and non-linear associations. Of the patients, 56.7% (1,355/2,388) developed AKI. While a simple linear association between GPR and AKI was not significant after adjusting for confounders (P = 0.20), we discovered a significant non-linear "J-shaped" relationship (P for non-linearity = 0.012). The risk of AKI increased steeply once GPR surpassed an inflection point of approximately 30. A random forest model incorporating multiple clinical variables demonstrated significantly superior predictive performance (AUC = 0.808) compared to traditional logistic regression (AUC = 0.785; DeLong test P = 0.025). These findings reveal that a high GPR (> 30) acts as an independent non-linear risk indicator for post-TBI AKI, Rather than a direct driver of injury, an elevated GPR represents a valuable early warning signal for metabolic decompensation, suggesting clinicians should closely monitor high-risk patients to facilitate early recognition of AKI.