Reducing multiple-breath washout test burden in cystic fibrosis: agreement between the first acceptable trial and mean lung clearance index.

BACKGROUND: Lung clearance index (LCI) derived from multiple-breath washout (MBW) is a sensitive marker of early lung disease in cystic fibrosis (CF), but testing is limited by the need for repeated technically acceptable trials. Whether a single technically acceptable trial provides information comparable to conventional mean-based reporting remains uncertain. METHODS: We performed a retrospective pooled analysis of MBW test occasions from three multicenter cohorts (TRACK, SIMPLIFY, and PROSPECT), including children and adults with CF and healthy controls. Agreement between the first technically acceptable LCI and mean LCI from two and three acceptable trials was assessed using intraclass correlation coefficients and Bland-Altman analysis. Concordance relative to age-dependent upper limits of normal was also evaluated. RESULTS: A total of 1960 MBW test occasions from 466 participants were included. Allowing a single technically acceptable trial increased overall test acceptability by 3.6%, recovering 78 additional test occasions. Agreement between the first technically acceptable trial and mean LCI from two trials was high (ICC 0.992; mean bias -0.03 LCI units; limits of agreement -0.67 to 0.60). Similar agreement was observed versus the mean of three trials (ICC 0.989; bias -0.06; limits of agreement -0.80 to 0.68). Findings were consistent across cohorts, age groups, and clinical state. CONCLUSIONS: Across three independent cohorts, the first technically acceptable MBW trial showed close agreement with mean-based LCI reporting. A single-trial approach may reduce MBW test burden while preserving clinical interpretability in selected contexts.