Biomarkers in exhaled breath condensate: a review of collection, processing and analysis

Abstract

Exhaled breath condensate (EBC) is a potential rich source for countless biomarkers that can provide valuable information about respiratory as well as systemic diseases. EBC has been studied in a variety of diseases including allergic rhinitis, asthma, chronic obstructive lung disease, cystic fibrosis, lung cancer, and obstructive sleep apnea syndrome. Although numerous biomarkers have been discovered and studied in EBC, the methods of collection and biomarker detection have not been fully standardized. While leaving standardization methods up to individual labs for the present time is optimal for the continued discovery of new biomarkers in EBC, this decreases the reproducibility and generalizability of the findings. In this review we will discuss specific biomarkers studied in specific diseases as well as some of the related technical issues including collection, processing and analysis.

Figure 1

Exhaled breath condensate schematic. As the individual inhales, air flows into the device, bypassing the cooling sleeve, as indicated by the white arrow. During exhalation air moves out through the cooling chamber as indicated by the black arrows.

Figure 2

Phase diagram illustrating the lyophilization process in detail. Figure adapted from Labconco protocol on freeze-drying [135]. Most samples are frozen below the point at which the entire suspension is completely frozen (eutectic point) (X) and raised to just below the critical temperature (Y). The pressure is lowered (Z) to encourage the free flow of water molecules from the product. The collecting system of the lyophilizer acts as a cold trap with a low temperature (W) to collect moisture, leaving the frozen sample.