The neutrophil-to-lymphocyte ratio (NLR) is an inexpensive biomarker of systemic inflammation. Although widely studied in acute and chronic conditions, evidence on long-term outcomes in hospitalized older adults is limited. We assessed whether admission NLR predicts in-hospital and post-discharge all-cause mortality in geriatric patients. We performed a retrospective multicenter cohort study of acute medical admissions across IRCCS INRCA geriatric hospitals in Italy (January 2020-December 2024). Data were retrieved from electronic health records and laboratory databases. We analyzed 16,099 hospitalizations from 10,826 patients aged ≥65 years (median 84, 48% male). For long-term outcomes, 9,812 patients discharged alive after their first admission were followed up to 48 months. Admission NLR was calculated from complete blood counts; thresholds were defined by ROC analysis. Outcomes were in-hospital and 48-month mortality. Discrimination was assessed using AUC, Kaplan-Meier curves, and Cox proportional hazards models adjusted for demographics, comorbidities, and laboratory variables. In-hospital mortality occurred in 1,744 cases (11%). An NLR ≥5.36 was associated with higher in-hospital mortality (HR: 2.287; 95% CI: 2.025-2.582; p<0.001). For long-term outcomes, an NLR ≥5.05 predicted increased 48-month mortality (51.6% vs 26.3% for NLR <5.05; adjusted HR: 1.423; 95% CI: 1.302-1.556; p<0.001). NLR values increased with age and were higher in males ≥80 years. A dynamic rise in NLR was observed before in-hospital death, suggesting utility as a marker of deterioration. Admission NLR is a strong, independent predictor of short- and long-term mortality in older adults. Its simplicity supports risk stratification, though optimal cut-offs require validation.
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