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

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 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 99.6% 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.

Published on: 2012-11-16

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