Abstract Background Bronchiolitis obliterans syndrome (BOS) is a serious and potentially life-threatening pulmonary complication following allogeneic hematopoietic stem cell transplantation (HSCT). It is characterized by progressive, irreversible airflow obstruction due to small airway inflammation and fibrosis. In pediatric populations, the diagnosis of BOS remains particularly challenging due to limitations in pulmonary function testing and the applicability of adult-based diagnostic criteria. Objective To evaluate the clinical utility and sensitivity of pediatric-specific BOS diagnostic criteria in comparison to existing adult-based frameworks, with a focus on implications for early detection and management in children post-HSCT. Methods Historically, the National Institutes of Health (NIH) criteria for BOS have relied on absolute thresholds for FEV1, a decline in the FEV1/FVC ratio, absence of infection, and radiographic evidence of air trapping. However, these criteria often lack sensitivity in children, secondary to adaptation of adult criteria to pediatric patients. The International Society for Heart and Lung Transplantation (ISHLT) defines chronic lung allograft dysfunction (CLAD) post-lung transplant as either restrictive or obstructive, with a ≥ 20% decline in FEV1, offering a broader framework but still not tailored to pediatric HSCT recipients. To address these limitations, the American Thoracic Society (ATS) recently proposed pediatric-specific BOS criteria that incorporate relative changes in lung function rather than fixed thresholds. These criteria aim to improve diagnostic accuracy in children by accounting for developmental variability and the challenges of testing in medically complex populations. Results We performed a retrospective analysis of spirometry and clinical data from three pediatric transplant centers—University of Minnesota (UMN), Cincinnati Children’s Hospital Medical Center (CCHMC), and Children’s Hospital of Philadelphia (CHOP)—spanning 2014-2023. The cohort included 544 patients aged 4-27 years, of whom 183 had at least two spirometry tests, including a baseline study. Sixty-one patients met initial inclusion criteria, defined as a ≥ 15% decline in FEV1 and/or an FEV1/FVC z-score -1.64. Among these, 17 met NIH BOS criteria, 33 met ISHLT CLAD criteria, and 38 met ATS pediatric BOS criteria. Conclusion The ATS pediatric BOS criteria identified more cases than either NIH or ISHLT criteria, suggesting improved sensitivity. Notably, not all patients meeting diagnostic thresholds were clinically diagnosed with BOS, underscoring the need for prospective studies to validate these criteria and to better understand the clinical implications of lung function decline following HSCT. These findings highlight the importance of adopting pediatric-specific frameworks to enhance early recognition and intervention, potentially improving long-term respiratory outcomes. This abstract is funded by: none
Goldfarb et al. (Fri,) studied this question.