Biomarkers in pediatric asthma: clinical maturity, intended use, and future directions

Asthma in children is heterogeneous, and symptom-based assessment alone does not fully capture airway inflammation, future risk, or treatment responsiveness. A wide range of biomarkers has therefore been investigated, from clinically accessible inflammatory markers to emerging molecular and omics-based signatures. This narrative review, supported by a structured PubMed search, synthesizes pediatric asthma biomarker studies according to biomarker type, intended clinical use, feasibility in children, clinical maturity, and current limitations. FeNO and blood eosinophil count are the most clinically mature biomarkers, particularly for identifying type 2 inflammation and supporting selected decisions regarding anti-inflammatory treatment or biologic therapy. IgE sensitization provides important phenotypic context for allergic asthma and anti-IgE treatment selection, whereas induced sputum offers direct airway inflammatory phenotyping but remains limited to specialist settings. Eosinophil granule proteins, especially eosinophil-derived neurotoxin, may reflect eosinophil activation rather than eosinophil number alone, but require further assay harmonization and pediatric reference ranges. Other biomarkers, including periostin, cytokines, inflammatory proteins, microRNAs, breath-based markers, metabolomic and proteomic signatures, microbiome profiles, and multi-omics approaches, remain largely exploratory. Mechanistic studies highlight the importance of epithelial, immune, microbial, genetic, epigenetic, metabolic, and remodeling pathways in pediatric asthma endotyping. However, most emerging biomarkers are not yet clinically actionable. Future biomarker development should focus on clearly defined intended uses, age-appropriate validation, standardized assays, reproducible cutoffs, and evidence that biomarker-guided decisions improve outcomes beyond conventional clinical assessment, lung function, FeNO, blood eosinophils, and allergen sensitization.