Objective: The aim of this study was to (1) investigate the possibility to use urates in exhaled breath condensate (EBC) as a biomarker of airway inflammation and control in childhood asthma and (2) explore their association with other biomarkers of airway inflammation and clinical indices of asthma control (Asthma Control Test [ACT], quality of life [PAQLQ], lung function, prn beta-agonist use, time from last exacerbation [TLE].
Methods: This cross-sectional study comprised 103 consecutive patients (age 6-18 years) divided in groups of uncontrolled ([NC], n = 53) and controlled asthma ([C], n = 50). Measured lung function and biomarkers included: spirometry, eosinophilic cationic protein (ECP), high-sensitivity C-reactive protein (hs-CRP), exhaled NO (FENO), pH and urates in EBC and exhaled breath temperature (EBT).
Results: Statistically significant differences were found between groups for EBC urates, EBC pH and EBT (NC versus C: EBC urates, median [IQR], µmol/L; 10 [6] versus 45 [29], p < 0.001; EBC pH, mean [SD], 7.2 [0.17] versus 7.33 [0.16], p = 0.002; EBT mean [SD], °C; 34.26 [0.83], versus 33.90 [0.60], p = 0.014). EBC urates showed significant association with TLE and FENO (r = 0.518, p < 0.001; r = 0.369, p = 0.007, respectively) in NC, and EBC pH (r = 0.351, p < 0.001), FEV1 (r = 0.222, p = 0.024), ACT (r = 0.654, p < 0.001), PAQLQ (r = 0.686, p < 0.001) and prn salbutamol use (r = -0.527, p < 0.001) in all asthmatics.
Conclusion: In our study, EBC urates were found to be the best single predictor of asthma control and underlying airway inflammation. Our results provide evidence supporting the potential utility to use EBC urates as an additional non-invasive biomarker of control in childhood asthma.
Keywords: Biomarkers; EBC; FENO; childhood asthma; hs-CRP; inflammation.