Published ahead of print on February 23, 2006, doi:10.1164/rccm.200506-975OC Am. J. Respir. Crit. Care Med., Volume 173, Number 10, May 2006, 1106-1113 A more recent version of this article appeared on May 15, 2006
Submitted on June 24, 2005 Variability of Spirometry in Chronic Obstructive Pulmonary Disease: Results from Two Clinical TrialsLaura B Herpel1*,1 Pulmonary and Critical Care Medicine, The Johns Hopkins University School of Medicine, Baltimore, MD, USA, 2 Pulmonary and Critical Care Medicine, University of Utah School of Medicine, Salt Lake City, UT, USA, 3 Center for Clinical Trials, The Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA, 4 Pulmonary and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, USA, 5 Biostatistics, University of Minnesota School of Public Health, Minneapolis, MN, USA * To whom correspondence should be addressed. E-mail: lherpel{at}jhmi.edu.
Objective: Our goal is to determine short-term intra-individual biologic and measurement variability in spirometry of patients with a wide range of stable COPD severity, using datasets from The National Emphysema Treatment Trial (NETT) and Lung Health Study (LHS). This may be applied to determine criteria that can be used to assess a clinically meaningful change in spirometry. Methods: 5886 participants from LHS and 1215 participants from NETT performed pre-bronchodilator spirometry during two baseline sessions. We analyzed varying criteria for absolute and percent change of FEV1 and FVC to determine which criterion was met by 90% of the participants. Results: The mean ± SD FEV1 for the initial session was 2.64 ± 0.60 L, (75.1 ± 8.8 percent predicted) for LHS and 0.68 ± 0.22 L, (23.7 ± 6.5 percent predicted) for NETT. The mean ± SD number of days between test sessions was 24.9 ± 17.1 for LHS and 85.7 ± 21.7 for NETT. As the degree of obstruction increased, the intersession percent difference of FEV1 increased. However, the absolute difference between tests remained relatively constant despite the severity of obstruction (0.106 ± 0.10 L). Over 90% of participants had an intersession FEV1 difference less than 225 ml irrespective of the severity of obstruction. Conclusions: Absolute changes in FEV1 rather than percent change should be used to determine whether patients with COPD have improved or worsened between test sessions. Key words: spirometry, reproducibility of measurements, obstructive lung diseases, forced expiratory volume, vital capacity
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