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Lexington, KY
Dr. Mannino is affiliated with the Division of Pulmonary, Critical Care and Sleep Medicine, University of Kentucky Medical Center.
Correspondence to: David M. Mannino, MD, FCCP, Division of Pulmonary, Critical Care and Sleep Medicine, University of Kentucky Medical Center, 740 S Limestone St, K-528 Kentucky Clinic, Lexington, KY 40536; e-mail: dmannino{at}uky.edu
The Global Initiative on Obstructive Lung Disease (GOLD) criteria for COPD were developed in 20011 to provide a framework for the uniform diagnosis and staging of COPD, and have been recently updated.2 These criteria have been, in large part, incorporated into the COPD guidelines of the American Thoracic Society and the European Respiratory Society.3 While there are several components of these COPD criteria that remain controversial, one of the biggest ones relates to GOLD stage 0 COPD, which comprises patients who are "at risk" for the development of COPD. The range of opinions on GOLD stage 0 vary from "is of little help in identifying subjects at risk for COPD,"4 to "... (having) a high demand for medical assistance,"5 to "... (being) associated with an increased mortality risk among male smokers."6
One area of controversy in this arena is whether GOLD stage 0 COPD really exists. Can a patient really have "chronic obstruction" with normal lung function? Earlier definitions of COPD required the presence of chronic respiratory symptoms in addition to some evidence of impaired lung function.7 We know from survey data that a large proportion of people with impaired lung function do not report respiratory symptoms and that a large proportion of people with respiratory symptoms have normal lung function.8
Another area of controversy relates to the symptoms that are actually needed to define GOLD stage 0. Some authors4 have required the presence of symptoms of chronic bronchitis that were used in the previous definitions of COPD (ie, at least 3 months annually of chronic cough productive of sputum). Others9 have used a more sensitive definition (ie, the presence of any respiratory symptom that occurs on a frequent basis, such as cough, sputum, wheeze, or dyspnea).
Whether or not GOLD stage 0 COPD, once defined, is actually clinically relevant is another question. (An article by Vestbo et al4 suggested that objective evidence of COPD in patients with GOLD stage 0 COPD, defined in that population as people with chronic bronchitis with sputum production, was not more likely to develop.) Other articles,5910 though, have suggested that respiratory symptoms predict increased morbidity, the development of COPD, and mortality independently of lung function.
The article by Stavem et al11 in this issue of CHEST (see page 318) looked at several of the issues relating to the definition and outcomes of GOLD stage 0 COPD. In their primary analysis, Stavem et al11 defined GOLD stage 0 COPD as occurring in people with normal lung function but a positive response to the question "do you usually bring up phlegm (from your chest) like this on most days for as much as 3 months each year?" This resulted in a nonsignificant increased adjusted risk of mortality (hazard ratio, 1.19; 95% confidence interval, 0.91 to 1.57). Surprisingly, when they used a more sensitive definition for GOLD stage 0 COPD of "any breathlessness, any phlegm, or recent increased cough and phlegm" the adjusted risk increased (hazard ratio, 1.35; 95% confidence interval, 1.11 to 1.64).
The evidence presented in this article suggests that respiratory symptoms predict mortality. In this study, a more sensitive definition resulted in a larger risk of death, which is the opposite of what one might expect to see, where a more inclusive definition includes people with milder disease. The reasons for this are unclear and may be related to the presence of comorbid diseases of the cardiovascular or musculoskeletal system, may be a marker for susceptibility to tobacco smoke, or may be related to other unknown or unmeasured factors.
To answer the questions posed in the title of this editorial, GOLD stage 0 is both real and matters, in that evidence is mounting that it predicts adverse outcomes. If one argues that the ability to predict adverse outcomes such as death is important, then the presence of respiratory symptoms, even in the setting of normal lung function, is also important. What patients with respiratory symptoms but normal lung function actually represent is unclear. Perhaps they represent a subtype of COPD. Perhaps they represent a form of "chronic exacerbation" in our patients in whom COPD has not yet developed. Perhaps they represent comorbid disease. Clinically, the presence of respiratory symptoms among people with normal lung function may provide an opportunity for interventions that will potentially improve both the quality and duration of life in our patients.
Footnotes
The author has accepted research funding from GlaxoSmithKline and Pfizer; speaking fees from GlaxoSmithKline, Pfizer, Ortho Biotech, and Dey; and is on advisory boards for GlaxoSmithKline, Pfizer, and Boerhringer Ingelheim.
References
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