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: = 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. Results: < 0.001). 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.