Table 1_Prognostic nutritional index at admission predicts 90-day mortality in patients aged ≥80 years with hip fracture: a system-level readout of the nutrition–immune milieu relevant to microenvironment-responsive bone repair.docx

BackgroundHip fractures in super-elderly patients are associated with high short-term mortality. The Prognostic Nutritional Index (PNI) is a simple marker reflecting both nutritional and immune status, but its prognostic value in super-elderly hip fracture patients remains unclear.
MethodsWe retrospectively included 614 patients aged ≥80 years with traumatic hip fractures from a tertiary hospital (n = 457) and the MIMIC-IV database (n = 157). PNI was calculated from serum albumin and absolute lymphocyte count measured within 24 h of admission. The optimal PNI cut-off for predicting 90-day all-cause mortality was determined using X-tile and used to define low- and high-PNI groups. Least absolute shrinkage and selection operator (LASSO) regression, Cox proportional hazards models, and propensity score matching (PSM) were applied to evaluate the association between admission PNI and 90-day mortality.
ResultsThe optimal PNI cut-off was 37.2, yielding 231 patients (37.6%) in the low-PNI group (PNI ≤ 37.2) and 383 (62.4%) in the high-PNI group (PNI > 37.2). Before PSM, patients with low PNI were older and had worse laboratory profiles, including lower hemoglobin, albumin, and lymphocyte counts. The 90-day mortality rate was significantly higher in the low-PNI than in the high-PNI group (21.65% vs. 9.40%, p < 0.001). LASSO identified sex, race, chronic pulmonary disease, hemoglobin, creatinine, and PNI as variables associated with 90-day mortality. After 1:2 PSM, 398 patients were retained with most baseline imbalances effectively reduced. In robust Cox proportional hazards analyses for the matched cohort, high PNI was associated with lower 90-day mortality in univariate models (HR 0.34, 95% CI 0.18–0.63; p < 0.001); Race violated the proportional hazards assumption; this association remained robust in the fully adjusted robust Cox model with race treated as a stratified variable (HR 0.34, 95% CI 0.19–0.63; p < 0.001).
ConclusionA low admission PNI (≤37.2) is strongly and independently associated with higher 90-day mortality in super-elderly patients with hip fractures. PNI, derived from routine laboratory tests within 24 h of admission, provides a simple and inexpensive tool for early risk stratification in this vulnerable population.