Abstract
BackgroundChronic Obstructive Pulmonary Disease (COPD) is defined by post-bronchodilator spirometry. Data on “normal values” come predominantly from pre-bronchodilator spirometry. The effects of this on diagnosis are unknown.MethodsLower limits of normal (LLN) were estimated from “normal” participants in the Burden of Obstructive Lung Disease (BOLD) programme. Values separately derived using pre- and post-bronchodilator spirometry were compared. Sensitivity and specificity of criteria derived from pre-bronchodilator spirometry and pre-bronchodilator spirometry adjusted by a constant were assessed in the remaining population. The “gold standard” was the LLN for the post-bronchodilator spirometry in the “normal population”. For FEV1/FVC, sensitivity and specificity of criteria were also assessed when a fixed value of < 70% was used rather than LLN.ResultsOf 6,600 participants with full data, 1,354 were defined as “normal”. Mean differences between pre- and post- bronchodilator measurements were small and the Bland-Altman plots showed no association between difference and mean value. Compared with using the gold standard, however, tests using pre-bronchodilator spirometry had a sensitivity and specificity of detecting a low FEV1 of 78.4% and 100%, a low FVC of 99.8% and 99.1% and a low FEV1/FVC ratio of 65% and 100%. Adjusting this by a constant improved the sensitivity without substantially altering the specificity for FEV1 (99%, 99.8%), FVC (97.4%, 99.9%) and FEV1/FVC (98.7%, 99.5%).ConclusionsUsing pre-bronchodilator spirometry to derive norms for lung function reduces sensitivity compared to a post-bronchodilator gold standard. Adjustment of these values by a constant can improve validity of the test.
Highlights
Chronic Obstructive Pulmonary Disease (COPD) is defined by post-bronchodilator spirometry
For forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) we looked at the extent of misclassification using criteria based on pre-bronchodilator spirometry and defining airway obstruction by FEV1/FVC
Using the spirometric classification of COPD based on post-bronchodilator FEV1, the distribution of the 5246 participants per GOLD class is; 4053 participants have no COPD i.e. FEV1/FVC(%) ≥ 70%, 633 have mild COPD, 461 have moderate COPD, 88 have severe COPD and 11 have very severe COPD
Summary
Chronic Obstructive Pulmonary Disease (COPD) is defined by post-bronchodilator spirometry. Data on “normal values” come predominantly from pre-bronchodilator spirometry. The effects of this on diagnosis are unknown. GOLD defines chronic pulmonary obstructive disease (COPD) in terms of post-bronchodilator lung function [1], but the data from which ‘normal values’ are derived are generally based on pre-bronchodilator lung function measures [2,3]. We assessed the extent to which any differences varied by age, body mass index and height for males and females, separately, and the extent of misclassification using criteria based on pre-bronchodilator spirometry. For FEV1/FVC we looked at the extent of misclassification using criteria based on pre-bronchodilator spirometry and defining airway obstruction by FEV1/FVC
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