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.

Background: Hip 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. Methods: We retrospectively included 614 patients aged ≥80 years with traumatic hip fractures from a tertiary hospital ( Results: The 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%, Conclusion: A 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.