Establishment of age-specific reference intervals for peripheral blood SII, NLR, PLR, and LMR in healthy children

To establish and validate age-specific reference intervals for the peripheral blood systemic immune-inflammation index (SII), neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and lymphocyte-to-monocyte ratio (LMR) in healthy children. A total of 2106 healthy children undergoing physical examination at The First People’s Hospital of Zigong from April 2023 to February 2025 were enrolled. Blood cell parameters were measured using the XN-1000 hematology analyzer, and SII, NLR, PLR, and LMR were calculated. The non-parametric method was employed to establish the 95% reference intervals. No statistically significant differences were observed in SII, NLR, PLR, or LMR between genders (P > 0.05). Participants were stratified into three age groups: 28 days to 2 years, 2 to 6 years, and 6 to 18 years. The established reference intervals for SII were 28.60 × 10⁹/L to 298.85 × 10⁹/L, 83.09 × 10⁹/L to 601.33 × 10⁹/L, and 140.02 × 10⁹/L to 657.19 × 10⁹/L, respectively, for the three age groups. The corresponding NLR reference intervals were 0.10–0.92, 0.35–1.88, and 0.57–2.30. PLR reference intervals were 29.39-115.15, 39.93-150.46, and 56.74-172.55. LMR reference intervals were 3.42–13.84, 2.81–13.03, and 2.41–10.56. A validation study conducted on 92 children from the Department of Child Health Care of the same hospital between April 2025 and September 2025 confirmed the applicability of these reference intervals. This indicates that the established reference intervals for peripheral blood SII, NLR, PLR, and LMR in children from the Zigong region are suitable for local clinical practice. This study is the first to establish reference intervals for NLR, PLR, SII, and LMR in children from the Zigong region, providing a basis for the assessment of inflammatory diseases in local pediatric populations.