Investigating the reproducibility of real time breath measurements using proton transfer reaction - time of flight - mass spectrometry for breath of volatile organic compounds in COPD Patients.

The potential of biomarkers in exhaled breath, present as volatile organic compounds (VOCs) has led to an increase in studies using exhaled breath as a part of the biomarker discovery process. The reproducibility of the VOC composition in breath samples from subjects with COPD is poorly understood and can be influenced by a number of factors such as diet, lifestyle and disease state. We undertook a single centre prospective study in subjects with moderate to severe COPD. Subjects were asked to provide 3 incentivized breath samples each 8 weeks apart whilst the patients were stable. The VOC profiles in the breath samples was assessed in real-time using Proton Transfer Reaction - Time of Flight - Mass Spectrometry (PTR-TOF-MS). Reproducibility (Intra-class correlation [ICC]) was determined for the common VOCs acetone and isoprene. Thirty-four COPD patients were studied of which twenty-six were men. The subjects had a mean (standard deviation [SD]) age 70 (66-74) years and FEV1% predicted 52 (32.2-52.3) %. The ICC coefficients (p=0.05) for the common VOCs acetone and isoprene were 0.820 (0.743 to 0.889) and 0.890 (0.846 to 0.936) respectively. VOC breath biomarker detection in COPD using PTR-TOF-MS is reproducible for common VOCs. The response of these biomarkers to changes in therapy or following exacerbations needs to be further investigated.