The analysis of exhaled breath condensate (EBC) in children is a challenging new technique and has potential as a noninvasive measure to assess and monitor airway inflammation, oxidative stress and metabolic processes. The technique is safe, simple to perform and ideally suited for young children and for repeated use in longitudinal studies.
Various collector systems have been described so far, all with the same principle of cooling the exhaled air with consequent condensation of water vapour as well as impacting aerosol particles to the cold surfaces. There is striking variability of results between different studies and laboratories. There are a number of important reasons for this variability. The concentration of most of the biomarkers in EBC is at the detection limit of the assays and there is a high risk of contamination of the EBC contents by the upper airways and from ambient sources. There is evidence that condenser coating surfaces and the temperature at which EBC is collected influence the biomarker concentration to a variable extent. An unresolved issue is the highly variable dilution of nonvolatile substances within the EBC, not only between subjects but also within a single subject over time. Several attempts have been made to overcome this important issue, but the practical difficulties of measuring both a biomarker and a dilution marker within the relatively small volume of EBC have limited widespread use of dilution correction. Many different biomarkers have been measured in EBC obtained from children with different respiratory diseases, most in a cross-sectional manner, with the aim of describing markers that allow distinction between health and disease and between different entities of respiratory disease. In this chapter, we provide a detailed update on the current knowledge of EBC contents and discuss the available paediatric data.