The association between hemoglobin‑to‑red cell distribution width ratio and short‑term mortality in patients with hip fracture: A retrospective study of the MIMIC-IV database

This study aimed to investigate the association between the hemoglobin to red cell distribution width ratio (HRR) and 90-day all-cause mortality in patients with hip fracture and evaluate its potential as a prognostic biomarker while analyzing the role of blood urea nitrogen (BUN) as a mediator in this relationship. This retrospective cohort study utilized data from the Medical Information Mart for Intensive Care IV database. Adult patients diagnosed with hip fracture based on ICD-9 and ICD-10 codes were included. The Boruta algorithm, a machine learning technique, was employed to screen for significant contributory clinical indicators. Multivariable logistic regression models were constructed to identify independent prognostic factors. Predictive performance was assessed via receiver operating characteristic curves and compared using the DeLong test. Finally, mediation analysis was conducted to explore the potential mediating role of BUN. A total of 1431 patients were included, comprising 1237 survivors and 194 non-survivors. The cohort was predominantly female (67.2%, n = 962). Patients in the non-survivor group were significantly older than those in the survivor group (median age: 89 interquartile ranges: 83.25–91.75 vs 81 interquartile ranges: 67–89 years, P < .001). The mean HRR was significantly lower in the non-survivor group compared to the survivor group (6.95 ± 1.47 vs 7.80 ± 1.55, P < .001). Multivariable analysis showed that after adjusting for confounding factors such as age, gender, creatinine, sodium, potassium, red blood cell count, and BUN, HRR remained an independent prognostic factor (OR = 0.728 0.605–0.876, P < .001). The predictive ability improved when HRR was combined with other clinical indicators (area under the curve = 0.783 0.751–0.815 vs HRR alone: area under the curve = 0.644 0.614–0.695). Mediation analysis indicated that BUN partially mediated the effect of HRR on 90-day mortality ( P < .001), accounting for 31.5% of the total effect. Lower levels of HRR are associated with higher 90-day all-cause mortality in patients with hip fracture, suggesting that HRR may be an effective biomarker for assessing short-term prognosis in these patients. BUN plays an important role as a mediator between HRR and 90-day mortality. Incorporating HRR into the initial assessment could help clinicians rapidly identify high-risk individuals at the bedside, enabling early targeted interventions to improve survival.