After a busy day in the primary care clinic, having finished the day’s dictations and called a patient to discuss the results of his lipid panel, Dr. B reviews tomorrow’s schedule, and notices 2 patients with a primary diagnosis of chronic obstructive pulmonary disease (COPD). Dr. B recalls a recent publication on changes in the classification of COPD by the Global Initiative for Chronic Obstructive Lung Disease (GOLD). 1 She remembers the main message being the degree of airway obstruction as measured by the forced expiratory volume in the first second (FEV 1) is now considered insufficient to classify COPD severity and to make a therapeutic decision. This paradigm shift contradicts the familiar concept that FEV 1 is the cornerstone piece of information in COPD, resulting in some degree of uncertainty about how to apply this in the practice. Dr. B. considers a multitude of practical questions, including: Is there a good reason to change the classification of COPD? How easy is it to use?
Will it make any therapeutic differences to my patients? In this article, the authors attempt to answer these and other questions prompted by the recent changes in the GOLD classification, with emphasis on its clinical use.
A Heterogeneous Condition
Spirometry is central to the diagnosis of obstructive lung diseases, including COPD and asthma. The diagnosis of COPD requires demonstration of an obstructive ventilatory defect in the spirometry, usually defined as a ratio of FEV1 to forced vital capacity (FVC) below 70% (FEV1/FVC < 0.7). FEV1 is still important, not only to confirm the diagnosis of airflow obstruction, but because it predicts mortality when severely reduced. However, during the last decade severity of airflow limitation has been challenged as a descriptor of both symptom burden and consequences of COPD by data from large studies. 2 For example, it has been demonstrated that 2 patients with the same degree of obstruction, measured by the FEV1 percentage predicted, can provide the physician with very different experiences about the impact of their disease in daily life. 3 These differences extend to the severity of their dyspnea; their exercise capacity, as seen in the sixminute walking distance test (6MWD); or their perceived quality of life (QOL), measured by the score on the Saint George’s Respiratory Questionnaire (SGRQ). These measures of disease impact show an extremely low correlation with FEV1: a correlation of 0.36 with the severity of dyspnea, 0.34 with 6MWD, and 0.38 with the SGRQ total score. 2 These newer studies imply that while spirometry is important, it captures only a small portion of the symptomatic and functional impact of COPD.
Increasing interest in understanding the differences between COPD subjects has been the main motivation in identifying distinct COPD phenotypes, subgroups of patients with similar disease experience, probable similar underlying pathogenic mechanisms, similar outcomes, and perhaps specific treatment alternatives. 4,5 The severity of airflow limitation, as measured by FEV1 percent predicted, is not always related with some of the emerging COPD phenotypes (eg, chronic bronchitis predominant phenotype, frequent exacerbation phenotype). 6-8 Chronic bronchitis can be present across the whole spectrum of spirometry severity, and is always associated with poorer QOL and worse clinical outcomes. Similarly, there are patients with frequent exacerbation phenotype (defined as ≥ 2 exacerbations/year) at every level of airflow obstruction, and the phenotype tends to be stable, meaning that previous frequent exacerbations are a good predictor of future exacerbations. 8