Can spirometric norms be set using pre- or post- bronchodilator test results in older people?

Background: 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.Methods: Lower 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.Results: Of 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%).Conclusions: Using 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.