Where are we with biomarkers in paediatric asthma in 2026?

Paediatric asthma is a heterogenous clinical syndrome where objective tests aid, but do not replace, clinical judgment. In 2026, the challenge is determining which biomarkers and tests are most informative for different patients and purposes. This review summarises current evidence supporting key diagnostic and monitoring tools for childhood asthma (age 5-16 years): exhaled nitric oxide fraction (F _ENO), spirometry with bronchodilator reversibility (BDR), and additional investigations such as peak expiratory flow variability, blood eosinophils, allergen sensitisation and bronchial challenge. Recent British Thoracic Society/National Institute for Health and Care Excellence/Scottish Intercollegiate Guidelines Network and European Respiratory Society guidelines emphasise the need for objective confirmation of asthma, but differ in the degree of diagnostic certainty and test prioritisation. F _ENO is now the leading inflammatory biomarker in routine paediatric care, valued for its noninvasive nature, ease and high specificity at elevated thresholds, especially for type 2 asthma. Its sensitivity, however, is modest, so it should not be relied upon as a stand-alone rule-out test. Spirometry remains a core physiological assessment, although its diagnostic accuracy alone is limited, and evidence supporting BDR thresholds in children is not robust. Additional tests should be used selectively, particularly when initial investigations are negative, discordant or technically challenging, or when severe asthma requires phenotype driven therapy. Biomarkers also play an important role in monitoring and severe asthma care, including predicting response to biologics. Emerging approaches like breathomics, alarmin-based biomarkers, and multi-omic profiling are discussed. Overall, biomarkers have enhanced the precision of paediatric asthma assessment, especially in severe cases, but their greatest value is in complementing, not replacing, thorough clinical evaluation.