Association Between Neutrophil-to-Lymphocyte Ratio and Early Detection of Ventilator-Associated Pneumonia in Mechanically Ventilated ICU Patients

Background: Ventilator-associated pneumonia (VAP) is a frequent and severe complication in mechanically ventilated intensive care unit (ICU) patients. Early diagnosis remains challenging, and reliable biomarkers for early prediction are still needed. The neutrophil-to-lymphocyte ratio (NLR), derived from routine blood tests, has emerged as a potential marker of systemic inflammation. This study aimed to evaluate the association between NLR dynamics and the development of VAP in mechanically ventilated patients. Methods: This study represents a secondary analysis of a prospective observational cohort conducted in a tertiary ICU. Adult patients requiring mechanical ventilation for more than 48 h were included. Microbiological sampling and blood tests were performed at predefined time points. In the study group, endotracheal tubes were systematically replaced at scheduled intervals, while the control group received standard management. NLR values were calculated from routine complete blood counts and analyzed in relation to the occurrence of VAP. Results: A total of 312 patients were included (162 in the study group and 150 in the control group). VAP incidence was significantly lower in the study group (27.27%) compared with the control group (56.7%) (χ2 = 26.81, p = 2.24 × 10−7). Patients in the study group who developed VAP had higher NLR values prior to clinical diagnosis. ROC analysis identified an optimal NLR cutoff of 8.26 for predicting VAP. In contrast, NLR did not demonstrate predictive value in the control group (AUC = 0.55). NLR showed limited discriminatory ability (AUC ≈ 0.62), only slightly above random classification. NLR showed a moderate correlation with CRP (ρ = 0.46, p < 0.001) and a weaker association with PCT. Conclusions: Elevated NLR values were associated with the subsequent development of VAP; however, the observed predictive performance was modest and context-dependent. These findings should be considered exploratory and require validation in future studies.