Stitching and switching: the impact of discontinuous lung function reference equations

To the Editors: In order to distinguish the effects of lung disease from those of normal growth and development, lung function is expressed in comparison with reference data, with forced expiratory volume in 1 s (FEV1) commonly being presented as % predicted. FEV1 % pred has been identified as being of prognostic value in cystic fibrosis (CF), such that an FEV1 of 20% from baseline determined by the average of two measurements made ≥3 weeks apart. Continuing to monitor FEV1 % pred after the development of BOS has also been shown to provide important insight into the patient’s prognosis and therapeutic options [2]. Given that FEV1 % pred plays such a key role in the clinical management of a child with CF or any child who has undergone lung transplantation, it is imperative to ensure that it is measured and interpreted accurately. Although guidelines for standardised measurement of spirometry have been developed for both adults [3] and children [4], the decision on which spirometry reference equation to use, amongst the plethora available [5], varies widely. This situation is further complicated by …