Adrenomedullin is a good marker of severity and prognosis in patients with bronchiolitis.

Acute bronchiolitis is a leading cause of pediatric hospital admissions, particularly during winter months, placing significant pressure on healthcare systems. Currently, the BROSJOD scale allows for severity stratification based on clinical variables. However, the incorporation of biomarkers could improve predictive capacity. The main purpose of this study is to analyze whether adrenomedullin (MR-proADM) can serve as a predictor of severity and prognosis in patients with bronchiolitis. A single-center, prospective, observational cohort study was conducted over two consecutive epidemic periods (2022-2024) at a tertiary care hospital. The study included hospitalized patients under 2 years of age presenting with an episode of acute bronchiolitis. Demographic variables, clinical severity score (BROSJOD), and laboratory parameters were systematically collected. MR-proADM levels were measured in urine for all patients and in plasma for patients requiring blood tests as part of standard care. Multivariate regression models and receiver operating characteristic (ROC) curves were utilized to evaluate the predictive value of MR-proADM levels and clinical score regarding different morbidity and mortality outcomes. A total of 107 patients were analyzed; given the small mild subgroup (n = 2), findings for these patients remain descriptive. Urinary MR-proADM levels were higher in patients with moderate and severe bronchiolitis. However, after normalization for urinary creatinine, the association disappeared, suggesting that the observed differences were largely influenced by urine concentration. Plasma MR-proADM levels at admission were identified as significant independent predictors for both the total duration of respiratory support and total hospital length of stay. Plasma MR-proADM was also a significant predictor of the need for fluid resuscitation (AUC 0.849) and the presence of bacterial coinfection (AUC 0.730). Notably, combining plasma MR-proADM with the admission BROSJOD score significantly enhanced predictive performance for the duration of respiratory support and fluid requirements compared to clinical scoring alone.Conclusion: Plasma MR-proADM emerges as a promising biomarker to complement clinical assessment in bronchiolitis at admission. Its integration with clinical scoring systems, including the BROSJOD scale, may enhance early risk stratification and help identify infants at increased risk of a severe clinical course or bacterial coinfection. However, in this cohort, urinary MR-proADM showed limited prognostic contribution after adjustment for urine concentration. These findings support the potential clinical utility of plasma MR-proADM to guide early decision-making and optimize resource use. Multicenter validation is needed to confirm generalizability and define clinically actionable thresholds. What is known? • MR-proADM is a biomarker with prognostic value in infectious and respiratory diseases, but its role in pediatric bronchiolitis, particularly when measured in urine, remains poorly defined. • Clinical scores such as BROSJOD are useful for assessing bronchiolitis severity, althougn additional biomarkers could improve risk stratification. What is new? • Plasma MR-proADM emerges as a robust prognostic biomarker independently predicting prolonged hospital stays, bacterial respiratory coinfection, and the need for respiratory, fluid, and inotropic support; its integration with standardized clinical scoring systems, such as the BROSJOD scale, could enhance early risk stratification. • Urinary MR-proADM increases with bronchiolitis severity; however, this association becomes less consistent after adjustment for urinary creatinine, highlighting the need for further evaluation of its interpretation and standardization.