Exhaled breath condensate hydrogen peroxide, pH and leukotriene B4 are associated with lower airway inflammation and airway cytology in the horse

Summary Background Exhaled breath condensate (EBC) analysis is a noninvasive method to assess the lower respiratory tract. In human subjects, EBC hydrogen peroxide (H2O2), pH and leukotriene B4 (LTB4) are useful for detection and monitoring of inflammatory lung diseases, including asthma. Objectives To determine associations between EBC biomarkers and cytological and endoscopic definitions of lower airway inflammation (LAI) while controlling for sampling and environmental variables. Study design Prospective, cross‐sectional study. Methods Clinical, endoscopic and airway cytological findings from 47 horses were compared with EBC pH and concentrations of H2O2 and LTB4 by univariate and multivariable analyses. Dichotomous (presence/absence of airway inflammation) and continuous outcome variables (differential cell counts in tracheal aspirate and bronchoalveolar lavage fluid, BALF) were evaluated and potential effects of collection and methodological factors were included. Results EBC pH and H2O2 concentrations were higher in horses with LAI and both were positively associated with the percentage of neutrophils in BALF (P