Repeatability of sodium and chloride in exhaled breath condensates

Exhaled breath condensate (EBC) has been proposed as a noninvasive tool to study airway inflammation. The reproducibility of breath condensates was recently questioned. We therefore measured sodium and chloride concentrations in EBC and assessed the repeatability of these measurements in healthy adults and children with airway disease. We investigated technical repeatability and within-day repeatability in five healthy adults, and compared these results with those of 10 asthmatic children and 9 children with cystic fibrosis (CF). We also assessed within-period repeatability in the healthy controls. We report that the variability of measurements was similar for within sample, within day, and between visits, for both normals and children with asthma and CF, and that the major source of variability of sodium and chloride measurements is restricted by the reproducibility of the measurement assay method used. The wide use of EBC is more likely to depend on the development of highly sensitive and reproducible assays, rather than further refinements of the collection technique.