Complex Biological Patterns of Soluble Cytokines and CD163 in Childhood Necessitating Age-Specific Reference Intervals for Evidence-Based Clinical Interpretation.

Background: Cytokine measurements to support clinical laboratory and research investigations have become increasingly common in pediatrics. However, there is a paucity of accurate pediatric reference intervals (RIs) essential to the interpretation of cytokine results. To address this gap, here, we establish age- and sex-specific pediatric reference values for clinically relevant inflammatory markers including CD163, and the cytokines IL18, IL-6, IL-10, IL-18, TNF-alpha, IFN-gamma, and CXCL-9. Methods: Healthy children and adolescents (n = 311, 1-19 years) were recruited as part of the Canadian Laboratory Initiative on Pediatric Reference Intervals (CALIPER) study. Multi-analyte measurements in plasma and analytical performance verification were conducted on the ProteinSimple (R) EllaTM automated immunoassay platform (Bio-Techne, MN, USA). Age- and sex-specific RIs were calculated based on Clinical and Laboratory Standards Institute guidelines. Additionally, 75th and 95th percentile cut-offs were determined. Results: Three types of reference value distributions were observed: (a) consistent levels throughout age and sex: IL-6, and IFN-gamma, (b) gradual decline in concentration with age: CD163, TNF-alpha, CXCL-9, and IL-10, (c) significantly higher concentrations during ages 4-14 years than earlier and later ages: IL-18 and IL-18. Reference values for CXCL-9, IL-10, and TNF-alpha under 8 years of age differed significantly from older children. CD163, IL-18 and IL-18 required three age partitions. CD163 demonstrated significant sex differences in ages 8-13 years. Conclusion: The circulating profile of cytokines in children is complex and can vary by age and sex. This necessitates careful interpretation of test results based on age and/or sex specific RIs facilitating more accurate clinical decision making.