Association between Neutrophil-to-Albumin Ratio and 28-Day All-Cause Mortality in Patients with Traumatic Brain Injury : A Retrospective Analysis of the MIMIC-IV Database.

Abstract

Objective: The neutrophil-to-albumin ratio (NAR) has emerged as a novel prognostic biomarker in multiple disease contexts, including infectious and cardiovascular disorders. Its prognostic relevance in traumatic brain injury (TBI), however, remains unexamined. This study investigates the association between NAR and 28-day all-cause mortality in patients with TBI.

Methods: This retrospective study analyzed data from the MIMIC-IV database. Neutrophil counts, serum albumin concentrations, and NAR values were recorded within the first 24 hours following TBI admission. Additional clinical and laboratory parameters were collected. The Youden index was employed to determine the optimal NAR threshold. Receiver operating characteristic (ROC) curve analysis was used to assess the discriminative capacity of NAR for all-cause mortality. Subgroup analyses were conducted to evaluate potential heterogeneity in NAR's prognostic utility across distinct patient subsets. An external validation cohort comprising 112 TBI cases from the institutional database was included to confirm predictive performance. Kaplan-Meier survival analyses were used to compare outcomes between high- and low-NAR groups, while ROC analysis was performed across the entire TBI cohort to assess overall prognostic accuracy.

Results: A total of 213 TBI patients were included and stratified based on 28-day survival status : 180 survivors and 33 non-survivors, resulting in an overall mortality rate of 15.5%. Multivariate Cox regression identified NAR as an independent predictor of 28-day all-cause mortality (hazard ratio [HR], 3.224; 95% confidence interval [CI], 1.321-4.594; p<0.001). ROC curve analysis determined an optimal NAR cutoff of 1.2839 for discriminating between survivors and non-survivors. Kaplan-Meier survival analysis revealed significantly elevated mortality among patients with NAR ≥1.2839 compared to those with NAR <1.2839 (log-rank p<0.001). The area under the curve (AUC) for NAR reached 82.45% (95% CI, 67.02-87.50%), surpassing the predictive performance of neutrophil count (AUC, 60.27%) and serum albumin level (AUC, 60.91%) when assessed individually. Subgroup analyses showed no significant interaction effects (p for interaction, 0.302-0.908), indicating consistent predictive performance across patient subgroups. External validation reinforced the prognostic value of NAR : patients in the high-NAR group demonstrated significantly worse survival outcomes (HR, 3.611; 95% CI, 1.385-9.419; p<0.01), with comparable discriminatory accuracy (AUC, 82.91%; 95% CI, 65.13-89.59%).

Conclusion: NAR functions as an independent and robust prognostic indicator of 28-day all-cause mortality in patients with TBI. Compared to neutrophil count and serum albumin levels alone, NAR demonstrates superior predictive accuracy and may serve as a valuable biomarker for early mortality risk stratification in this population.