Clinical utility of lung diffusing capacity for carbon monoxide (DLco) in children: a retrospective single-center study

Background: Diffusing capacity for carbon monoxide (DLco) testing is widely used in adult respiratory medicine, but its role in pediatric care remains unclear. This study aimed to assess the diagnostic and clinical utility of DLco testing in children at a single tertiary center. Methods: We conducted a retrospective analysis of DLco and spirometry data from all children who underwent pulmonary function testing at the University Children's Hospital Zurich between 2015 and 2025. Tests meeting ATS/ERS quality criteria (Grades A/B) and performed alongside same-day blood counts were included. Patients were categorized as undergoing initial diagnostic evaluation or follow-up monitoring. Results: Out of 269 DLco tests from 202 patients (median age 13.4 years), 72 tests (26.7%) were excluded due to insufficient quality. The final cohort included 197 tests from 144 patients. Among 54 children undergoing DLco as part of initial assessment, none had abnormal values or changes in diagnosis or management. In the follow-up group (n = 90), 16 patients (8.1%) had DLco z-scores below the lower limit of normal, but these findings did not influence clinical decisions. No significant correlation was observed between DLco and FEV1 z-scores (p = 0.399). Longitudinal data from 31 patients showed no significant changes in DLco. Conclusions: DLco testing in children is technically challenging, with a high proportion of tests failing quality standards. Abnormal results were rare and did not impact clinical management. These findings suggest limited routine utility for DLco in pediatric populations, underscoring the need for targeted indications and further prospective research.