Diagnostic Value Of Neutrophil-To-Lymphocyte And Platelet-To-Lymphocyte Ratios İn Early- And Late-Onset Neonatal Sepsis: A Retrospective Single-Centre Observational Study

Background Neonatal sepsis remains a leading cause of morbidity and mortality worldwide despite advances in perinatal and intensive care. Early and accurate diagnosis is challenging because clinical signs are often nonspecific and no single biomarker has shown perfect sensitivity and specificity. In recent years, complete blood count–derived indices such as the neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) have been proposed as inexpensive, readily available markers of systemic inflammation. This study aimed to evaluate the diagnostic value of NLR and PLR in early-onset (EOS) and late-onset sepsis (LOS) compared with jaundiced and healthy neonates, and to compare their performance with that of procalcitonin (PCT) and C-reactive protein (CRP). Methods In this retrospective single-centre study, we reviewed the records of neonates hospitalised in a level III neonatal intensive care unit between March 2022 and March 2025. A total of 446 infants were classified into four groups: EOS (first 3 postnatal days), LOS (≥ 4th day), jaundice without sepsis, and healthy controls. Pre-treatment laboratory data, including complete blood count, CRP and PCT, were extracted. NLR and PLR were calculated by dividing absolute neutrophil and platelet counts by lymphocyte counts, respectively. Group comparisons were performed using non-parametric tests. Receiver operating characteristic (ROC) curve analysis was used to assess the diagnostic performance of each biomarker for differentiating sepsis-positive (EOS + LOS) from sepsis-negative (jaundice + healthy) infants. Results Of the 446 neonates, 143 (32.1%) had EOS, 101 (22.6%) had LOS, 102 (22.9%) were in the jaundice group and 100 (22.4%) were healthy controls. Median NLR values were significantly higher in the EOS group than in the LOS, jaundice and healthy groups (1.97 vs 0.71, 0.84 and 0.67, respectively; p < 0.001). PLR values did not differ significantly between the four groups (p > 0.05). When EOS and LOS were combined as the sepsis-positive group, median NLR was higher in sepsis-positive than in sepsis-negative infants (1.34 vs 0.79; p < 0.001). In ROC analysis, PCT showed the highest diagnostic accuracy for sepsis (area under the curve [AUC] 0.97), followed by CRP (AUC 0.75) and NLR (AUC 0.65), whereas PLR had limited discriminative ability (AUC 0.54). Conclusions NLR is moderately useful for predicting neonatal sepsis, particularly in EOS, and may serve as a supportive parameter when interpreted alongside PCT, CRP and clinical findings. In this cohort, PLR did not provide meaningful additional diagnostic value. The combined use of CBC-derived ratios and conventional biomarkers may support early decision-making and help reduce unnecessary antibiotic exposure in neonates.