Exhaled breath condensate in asthma: from bench to bedside

The need for non-invasive assessment of airway inflammation is imperative, since inflammatory airway diseases, such as asthma and COPD, are characterized by variation in their clinical presentation throughout their course. Exhaled breath condensate (EBC) collection represents a rather appealing method that can be used to conveniently and noninvasively collect a wide range of volatile and non-volatile molecules from the respiratory tract, without affecting airway function or inflammation. Although promising, EBC is currently used only as a research tool, due to the lack of appropriate standardization and the absence of reference values. A large number of mediators of inflammation, oxidative and nitrosative stress, including adenosine, ammonia, hydrogen peroxide, isoprostanes, leukotrienes, prostanoids, nitrogen oxides, peptides and cytokines, have been studied in EBC. This review focuses mainly on the presentation of the above biomarkers in asthma as well as on the effect of various factors on their concentrations. Concentrations of such mediators have been shown to be related to the underlying asthma and its severity and to be modulated by therapeutic interventions. Despite the encouraging positive results up-to-date, the introduction of EBC in everyday clinical practice requires the work-out of some methodological pitfalls, the standardization of EBC collection, and finally the identification of a reliable biomarker which is reproducible, has normal values and provides information for the underlying inflammatory process and the response to treatment. So far none of the parameters studied in EBC fulfils the aforementioned requirements.