Objective To establish reference intervals for the systemic immune-inflammation index (SII), neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), lymphocyte-to-monocyte ratio (LMR), and neutrophil-to-monocyte ratio (NMR) in the peripheral blood of children with pneumonia in Xi'an area and explore their diagnostic values.

Methods A total of 10 330 healthy children with physical examinations in the Department of Child Health Care of Xi'an Children's Hospital from January 2023 to October 2024 were selected as control group, and 450 hospitalized children diagnosed as pediatric pneumonia were selected as case group. Data of SII, NLR, PLR, LMR, and NMR were statistically analyzed to establish reference intervals for healthy children. Differences in SII, NLR, PLR, LMR, and NMR levels among different pneumonia groups and the healthy control group were compared. Multivariate Logistic regression analysis was used to identify predictive indicators for viral pneumonia. The diagnostic value of SII, NLR, PLR, LMR, and NMR levels in pediatric pneumonia was assessed by the receiver operating characteristic (ROC) curve.

Results Among the 450 children with pneumonia, children in the viral pneumonia group were significantly younger than those in the Mycoplasma pneumonia group and the bacterial pneumonia group (P < 0.05). No significant differences were observed in SII, NLR, PLR, LMR, and NMR levels between children of different genders within the same age group (P>0.05). Compared with the control group, the Mycoplasma pneumonia group and the bacterial pneumonia group exhibited significantly elevated SII, NLR, PLR, and NMR levels and decreased LMR levels (P < 0.05). The viral pneumonia group showed significantly higher PLR levels and lower LMR and NMR levels compared with the control group (P < 0.05). The Mycoplasma pneumonia group and the bacterial pneumonia group had significantly higher SII, NLR, PLR, and NMR levels and lower LMR levels than the viral pneumonia group (P < 0.05). Multivariate Logistic regression analysis revealed that among children with pneumonia, LMR served as one of the differentiating factors for diagnosing viral pneumonia from non-viral pneumonia, while SII and NMR were protective factors against viral infection in children with pneumonia. The ROC curve demonstrated that the optimal cut-off values for diagnosing pediatric non-viral pneumonia by SII, NLR, PLR, NMR and the combined indicators of SII+NLR and SII×NLR were 283.968, 1.181, 120.739, 4.742, 284.920 and 220.209, respectively, with corresponding area under the curve (AUC) values of 0.862, 0.853, 0.804, 0.823, 0.862 and 0.862, respectively.

Conclusion Establishing reference intervals for SII, NLR, PLR, LMR, and NMR in the peripheral blood of children holds certain reference values for the diagnosis, treatment, and clinical decision-making of pediatric infectious diseases.