In a recent issue of Thorax Gan et al¹ published a systematic review and meta-analysis of 14 reports which confirmed the strong association between COPD and biological markers of systemic inflammation. In six reports COPD was diagnosed by the presence of a ratio of forced expiratory volume in 1 second to forced vital capacity (FEV₁/FVC ratio) lower than 0.7. However, in the remaining eight studies this measure was not available, and the authors assumed that all participants in the lowest quartile of FEV₁% (and, in one study,² of FVC%) had a diagnosis of COPD. In these cases the corresponding highest quartile group served as control. Since a COPD diagnosis based on a decreased FEV₁/FVC ratio was lacking in eight reports, the possibility cannot be excluded that a certain number of patients included in the meta-analysis did not have COPD but, rather, a restrictive ventilatory defect. This could be particularly true for participants in the study by …