Diagnosis, assessment, and phenotyping of COPD: beyond FEV₁

Abstract

COPD is now widely recognized as a complex heterogeneous syndrome, having both pulmonary and extrapulmonary features. In clinical practice, the diagnosis of COPD is based on the presence of chronic airflow limitation, as assessed by post-bronchodilator spirometry. The severity of the airflow limitation, as measured by percent predicted FEV1, provides important information to the physician to enable optimization of management. However, in order to accurately assess the complexity of COPD, there need to be other measures made beyond FEV1. At present, there is a lack of reliable and simple blood biomarkers to confirm and further assess the diagnosis of COPD. However, it is possible to identify patients who display different phenotypic characteristics of COPD that relate to clinically relevant outcomes. Currently, validated phenotypes of COPD include alpha-1 antitrypsin deficiency, and "frequent exacerbators". Recently, a definition and assessment of a new phenotype comprising patients with overlapping features of asthma and COPD has been suggested and is known as "asthma COPD overlap syndrome". Several other phenotypes have been proposed, but require validation against clinical outcomes. Defining phenotypes requires the assessment of multiple factors indicating disease severity, its impact, and its activity. Recognition and validation of COPD phenotypes has an important role to play in the selection of evidence-based targeted therapy in the future management of COPD, but regardless of the diagnostic terms, patients with COPD should be assessed and treated according to their individual treatable characteristics.

Keywords: ACOS; COPD; asthma; diagnosis; phenotype.

Figure 1

Comparison of pulmonary dynamics in health and COPD showing tidal pressure-volume curves during rest (filled area) and exercise (open area). Notes: Reproduced with permission of Taylor & Francis Ltd (http://www.tandfonline.com). O’Donnell DE, Laveneziana P. The clinical importance of dynamic lung hyperinflation in COPD. COPD: Journal of Chronic Obstructive Pulmonary Disease. 2006;3(4):219–232. Abbreviations: EELV, end-expiratory lung volume; IC, inspiratory capacity; IRV, inspiratory reserve volume; P, pressure; RV, residual volume; TLC, total lung capacity; V, volume.

Figure 2

Sputum inflammatory mediators in patients with asthma and COPD having phenotypes for (A) eosinophilic airway inflammation and (B) non-eosinophilic airway inflammation. Horizontal and error bars set at geometric mean and 95% confidence interval. Notes: Reproduced with permission from S. Karger AG, Basel, Switzerland. Copyright ©2012 Bafadhel M, McCormick M, Saha S, et al. Profiling of sputum inflam matory mediators in asthma and chronic obstructive pulmonary disease. Respiration. 2012;83(1):36–44. Abbreviations: CCL, CC chemokine ligand; CXCL, CXC chemokine ligand; IL, interleukin; MMP, matrix metallopeptidase; TNF, tumor necrosis factor; TNFR, tumor necrosis factor receptor; VEGF, vascular endothelial growth factor.

Figure 3

Potential reasons for the high prevalence of overlap between COPD and asthma.

Figure 4

Proposal for a COPD assessment control panel of variables that relate to three domains of the disease – severity, activity, and impact. Notes: Adapted by permission from BMJ Publishing Group Ltd. Thorax. Agusti A, MacNee W. The COPD control panel: towards personalised medicine in COPD. Volume 68(7), pages 687–690. Copyright ©2013. Abbreviations: 6MWD, 6-minute walk distance; CAT, COPD Assessment Test; IC/TLC, inspiratory to total lung capacity ratio; mMRC, modified Medical Research Council Dyspnea Scale; PaO₂, arterial oxygen pressure.