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Commentary |

Definitions of Exacerbations: Does It Really Matter in Clinical Trials on COPD?

Tanja W. Effing, PhD; Huib A. M. Kerstjens, MD, PhD; Evelyn M. Monninkhof, PhD; Paul D. L. P. M. van der Valk, MD, PhD; Emiel F. M. Wouters, MD, PhD; Dirkje S. Postma, MD, PhD; Gerhard A. Zielhuis, PhD; Job van der Palen, PhD
Author and Funding Information

Affiliations: From the Department of Pulmonology (Drs. Effing, van der Valk, and van der Palen), Medisch Spectrum Twente, Enschede, the Netherlands; University Medical Center Groningen and the Department of Pulmonology, University of Groningen (Drs. Kerstjens and Postma), Groningen, the Netherlands; Julius Center for Health Sciences and Primary Care (Dr. Monninkhof), University Medical Center Utrecht, Utrecht, the Netherlands; the Department of Respiratory Medicine (Dr. Wouters), University Hospital Maastricht, Maastricht, the Netherlands; and the Department of Epidemiology, Biostatistics, and HTA (Dr. Zielhuis), Radboud University Nijmegen, Nijmegen, the Netherlands; and the Department of Research Methodology, Measurement and Data Analysis (Dr. van der Palen), University of Twente, Enschede, the Netherlands.

Correspondence to: Tanja Effing, PhD, Medisch Spectrum Twente, Department of Pulmonology, Haaksbergerstraat 55, 7513 ER Enschede, the Netherlands; e-mail: tanjaeffing@gmail.com


This research was supported by grants from the Dutch Asthma Foundation, the Netherlands.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.xhtml).


© 2009 American College of Chest Physicians


Chest. 2009;136(3):918-923. doi:10.1378/chest.08-1680
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Many definitions of COPD exacerbations are reported. The choice for a definition determines the number of exacerbations observed. However, the effect of different definitions on the effect sizes of randomized controlled trials is unclear. This article provides an overview of the large variation of definitions of COPD exacerbations from the literature. Furthermore, the effect of using different definitions on effect sizes (relative risk and hazard ratio) was investigated in a randomized controlled discontinuation trial of inhaled corticosteroids. The following definitions were applied: (1) unscheduled medical attention, (2) a course of oral corticosteroids/antibiotics, (3) deterioration in two major or one major and one minor symptom according to Anthonisen (referenced later), (4) a change in one or more symptoms, (5) a change in two or more symptoms, and (6) a combination of numbers 2 and 4. Relative risks for the exacerbation rate ranged from 1.19 to 1.49, and hazard ratios for time to first exacerbation ranged from 1.36 to 1.84 for the various definitions, varying from nonsignificant to significant. Because the definition of a COPD exacerbation has an impact on the effect size of interventions, there is an urgent need for concerted attempts to reach agreement on a definition of an exacerbation. Also, the exact definition to be used in a study should be specified in the protocol.

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