Background  Expired breath condensate (EBC) has never been used to explore the level of oxidative stress in idiopathic pulmonary fibrosis (IPF). Therefore, the aim of this study was to measure the levels of H₂O₂ and 8‐isoprostane, as biomarkers of oxidative stress, in the EBC of patients with IPF.

Materials and methods  We investigated 16 patients with IPF and 15 healthy subjects as the control group. The levels of H₂O_{2 and} 8‐isoprostane were measured in the EBC of all subjects and were compared between the IPF and control groups. In patients with IPF, H₂O_{2 and} 8‐isoprostane were further correlated with pulmonary function tests (PFTs), the resting pO₂ and the differential cell count from the bronchoalveolar lavage fluid (BALF).

Results  The mean (95%CI) concentration of H₂O₂ was increased in the patients with IPF compared with the normal subjects (0·36, 0·24–0·47 µM vs. 0·16, 0·10–0·23 µM, P = 0·003). The mean (95%CI) concentration of 8‐isoprostane was also increased in the patients with IPF compared with the controls (74, 38–110 pg mL⁻¹ vs. 33, 28–39 pg mL⁻¹, P = 0·02). In the patients with IPF, the diffusing capacity of the lung for carbon monoxide was negatively correlated with the levels of H₂O₂ in EBC (P = 0·03, r = −0·58). No other correlation was found between the oxidative stress markers in the EBC and PFT values, pO₂ or BALF cell count.

Conclusions  Our data suggest that H₂O_{2 and} 8‐isoprostane are increased in the EBC of patients with IPF. H₂O₂ may be correlated with the severity of the disease in IPF.