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Exhaled breath condensate: lessons learned from veterinary medicine

Exhaled breath condensate (EBC) describes any sample collected by cooling exhaled breath. Because the method of condensate collection is simple, non-invasive, repeatable and does not necessarily require patient cooperation, EBC is not only an interesting, but also challenging, biological sample. Despite a period of EBC research lasting for more than 15 years, there are still many open questions with respect to EBC collection and analysis, and many biomarkers are still awaiting careful validation. In veterinary research, EBC collection has been described in conscious animals including calves, pigs, horses, cats and dogs. Numerous studies performed in these domestic animals not only contributed substantially to the current knowledge about the potentials of EBC-based diagnoses but also demonstrated pitfalls in EBC collection, analysis and interpretation. This review summarizes information about the collection of EBC and the interpretation of EBC results, particularly with respect to proteins, leukotrienes, hydrogen peroxide, urea, ammonia and pH. Published data emphasize the need to standardize approaches to produce reproducible EBC data. Quantifying the concentration of the EBC component of interest exhaled in a defined volume of exhaled breath (instead of comparing concentrations of this component analysed in liquid EBC) is an important step of standardization that might help to overcome methodological limitations deriving from the EBC collection process. Although information is based on domestic animal studies, it contributes to the general understanding in EBC research—independent of any particular mammalian species—and opens new perspectives for further studies.