Methodological Issues and Possible Clinical Implications for Exhaled Breath Condensate pH in Asthma

Exhaled breath condensate (EBC) pH is a commonly studied biomarker which represents the acidity of the whole airway tract, including the lower and upper airways as well as oral cavity. Because neat, unprocessed EBC pH can be affected by environmental and end-tidal carbon dioxide, two further reproducible techniques have been developed to measure condensate acidity with several methodological, pathophysiological and environmental factors which may influence EBC pH. Airway acidification may contribute to various pathological features of asthma, therefore EBC pH may be a non-invasive, but unspecific clinical biomarker of this disorder. This review summarises the current knowledge on EBC pH in asthma focusing on methodological aspects and possible clinical applications.