Association Between Admission Complete Blood Count-Derived Inflammatory Markers and Mortality in Neonatal Intensive Care Unit Patients: A Retrospective Observational Study.

BACKGROUND: Complete blood count (CBC)-derived inflammatory markers are readily available, inexpensive indices of systemic inflammation. This study evaluated their association with mortality in a heterogeneous neonatal intensive care unit (NICU) population. METHODS: This retrospective observational study included neonates admitted to a mixed level II and III NICU between 2022 and 2026. Neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII) and systemic inflammatory response index (SIRI) were calculated from admission CBCs. Associations with in-hospital mortality were assessed using logistic regression and sensitivity analyses. Discriminatory performance was evaluated using receiver operating characteristic analysis. RESULTS: Among 530 neonates, 45 (8.5%) died. SII and SIRI were significantly lower in nonsurvivors, whereas NLR and PLR did not differ between groups. After adjusting for gestational age, PLR was associated with mortality (aOR, 0.381; 95% CI, 0.151-0.960; p = 0.041), whereas NLR, SII and SIRI were not. The PLR association persisted after additional adjustment for culture-confirmed early-onset sepsis (p = 0.039) but was attenuated and was no longer statistically significant when birth weight replaced gestational age (p = 0.065). Standalone discrimination was poor for all indices (AUCs, 0.517-0.609), although SII showed statistically significant, albeit weak, discriminatory performance (AUC, 0.609; 95% CI, 0.529-0.689; p < 0.01). CONCLUSIONS: Admission CBC-derived inflammatory indices showed limited associations with mortality and poor standalone discriminatory performance. The association between PLR and mortality was sensitive to the choice of adjustment variable and warrants confirmation in prospective multicentre studies.