AbstractObjectiveNasal biomarkers have potential to add objectivity to the clinical assessment of the child with bronchiolitis. We aim to study, if nasal caspase and high‐mobility group box 1 protein (HMGB1) levels differ between patients who were hospitalized and those discharged from the emergency department (ED), among patients with bronchiolitis.MethodsUsing an observational cross‐sectional study design, we recruited patients younger than 24 months presenting to the ED from September 1, 2015 to May 31, 2017 with a diagnosis of acute bronchiolitis. We described the patients’ clinical severity measured by the modified respiratory index score (RIS), and performed standardized collection and analysis of nasal caspase and HMGB1 levels.ResultsAmong 85 patients recruited, the median age was 5.0 months (interquartile range, IQR 3.3‐7.2) and the median modified RIS score was 3 (IQR 2‐4). Hospitalized patients had a 2.4‐fold higher HMGB1 level than patients who were discharged from the ED (2.558 μg/mL [IQR 1.038‐5.125] vs 1.056 μg/mL [IQR 0.409‐2.395], P = 0.0013). There was no difference in median caspase level between hospitalized and discharged patients. The Area Under the Receiver Operating Characteristics curve predicting hospitalization was 0.7021 for HMGB1 compared to 0.5709 for RIS in this bronchiolitis cohort.ConclusionsOur study findings show that nasal HMGB1 levels significantly differentiate between young children with bronchiolitis who were hospitalized compared to those fit for discharge. This exploratory study holds potential for future research on nasal HMGB1 for severity stratification in young children with acute bronchiolitis.