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Copyright ©ERS Journals Ltd 2008
Definition of COPD: based on evidence or opinion?
1 Centro di Fisiopatologia Respiratoria e dello Studio della Dispnea, Azienda Ospedaliera Santa Croce e Carle, Cuneo, 2 University of Genoa, Genoa, 3 CNR Institute of Clinical Physiology, Pisa, Italy. 4 Pulmonary Division, LDS Hospital, Salt Lake City, UT, 6 Harbor UCLA Medical Center, Torrance, CA, 10 Hankinson Consulting Inc., Valdosta, GA, 11 Spaulding Rehabilitation Hospital, Boston, MA, 12 Duke University Medical Center, Durham, NC, 13 University of Cincinnati, OH, 17 Pharmaceutical Research Associates Inc., Lenexa, KS, USA. 5 Hospital Clinic, Servicio de Pneumologia, Barcelona, 15 University of Barcelona, Barcelona, Spain. 7 Hospital for Sick Children, Toronto, ON, Canada. 8 Dept of Respiratory Medicine, University Maastricht, Maastricht, The Netherlands. 9 Department of Pediatric Clinical Physiology, Queen Silvias Children's Hospital, Gothenburg, Sweden. 14 University Hospitals Birmingham NHS Trust, Birmingham, UK. 16 University of Aarhus, Aarhus, Denmark.
To the Editors:
In 1986, the American Thoracic Society (ATS) first suggested a fixed ratio of forced expiratory volume in one second (FEV1) to forced vital capacity (FVC) <0.75 to define airflow obstruction 1. Subsequent ATS documents published in 1991 2 and 1995 3 generically defined airflow obstruction as a reduction of FEV1/FVC, without recommending any numerical cut-off point.
By contrast, the European Respiratory Society (ERS) guidelines 4 suggested the diagnosis of airflow obstruction be based on a ratio of FEV1 to slow vital capacity (VC) <88 and <89% of predicted in males and females, respectively. These values were not arbitrarily chosen as they roughly correspond to the lower 95th percentiles of frequency distributions of a healthy population. More importantly, they are consistent with the well-known decrease of lung elastic recoil and, by inference, of forced expiratory flow with ageing.
In 2001, the Global Initiative for Chronic Obstructive Lung Disease (GOLD) took a step back, defining chronic obstructive pulmonary disease (COPD) by a fixed FEV1/FVC <0.70 5. Since then, the enthusiasm for having new guidelines has led the scientific community to overlook the possible consequences of such a definition, even if it was already clear that it may be a source of falsely positive cases in the general population 6. This was confirmed in a study in the USA 7 evaluating the impact of different definitions of airflow obstruction on the epidemiology of COPD. Quoting Celli et al. 7, "differences may be large, altering population prevalence estimates of COPD by >200%". It is noteworthy that, using FEV1/FVC <0.70, the prevalence of COPD in individuals aged 
70 yrs would be 40%.
At variance with the GOLD guidelines, the recent ATS/ERS guidelines on lung function testing 8 stressed the use of lower limits of normality (LLN), i.e. the lower fifth percentile of the frequency distribution of a healthy population, to define pulmonary function abnormalities.
In a recent editorial published in the European Respiratory Journal, Mannino 9 took a strong position in favour of the fixed FEV1/FVC <0.70, claiming that it is easy to keep in mind, thus helping to remove the barriers to a widespread use of spirometry, and is more sensitive than LLN to identify patients at risk of death and COPD-related hospitalisations 10.
We would like to draw the attention of the readers to the following critical issues.
First, the fixed cut-off point indicated by GOLD guidelines may have negative consequences by misclassifying healthy elderly subjects as COPD, thus possibly causing unnecessary treatment, and by misclassifying as healthy a number of subjects aged <50 yrs already affected by COPD 9, when something could be done to limit disease progression.
Secondly, the fact that risks of death and COPD-related hospitalisation 10 are predicted by FEV1/FVC <0.70 indicates that such an index may identify a proportion of individuals at risk 6, which has nothing to do with defining the diagnosis of the disease. Furthermore, it is an index which per se cannot reflect the severity of disease 8. This is clearly apparent if one keeps in mind that two patients with FEV1 of 20 and 100% pred may have the same FEV1/FVC <0.70 or even <LLN, depending on the associated reduction of FVC.
Thirdly, an FEV1/FVC >0.70 or even >LLN cannot exclude airflow obstruction with certainty because, in a minority of cases, FEV1 and FVC may be decreased proportionally as a result of an isolated increase in residual volume 8. This may lead to a false diagnosis of restriction instead of obstruction.
Fourthly, software and hardware have now changed the way of laboratory testing and there is no longer a need for manual, time-consuming calculations of predicted values, as even inexpensive spirometers can have predicting equations and statistically derived LLN values built in.
Finally, we understand that a fixed ratio might be useful where predicting equations are not available. However, the severity classification suggested by GOLD guidelines to tailor treatments, based on the percentage decrease from predicted FEV1 5, would be meaningless.
We are confident that with the world very rapidly "going global", the advancement of technology in the medical field will help to promote a larger use of lung function testing and, with it, the generation of reference equations for different countries and ethnicities. For the time being, however, we suggest that a definition of the pulmonary defects consistent with solid principles of lung physiology is maintained.
Statement of interest
None declared.
REFERENCES
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- Lung function testing. selection of reference values and interpretative strategies. American Thoracic Society. Am Rev Respir Dis 1991;144:1202–1218.[Web of Science][Medline] [Order article via Infotrieve]
- Standards for the diagnosis and care of patients with chronic obstructive pulmonary disease. American Thoracic Society. Am J Respir Crit Care Med 1995;152: Suppl. 5 S77–S121.
- Quanjer PH, Tammeling GJ, Cotes JE, Pedersen OF, Peslin R, Yernault J-C. Standardized lung function testing. Eur Respir J 1993;6:1–99.[Medline] [Order article via Infotrieve]
- Pauwels RA, Buist AS, Calverley PM, Jenkins CR. Hurd SS; GOLD Scientific Committee. Global strategies for the diagnosis, management, and prevention of chronic obstructive pulmonary disease. NHLBI/WHO Global Initiative for Chronic Obstructive Lung Disease (GOLD) Workshop summary. Am J Respir Crit Care Med 2001;163:1256–1276.
[Free Full Text] - Viegi G, Pedreschi M, Pistelli F, et al. Prevalence of airways obstruction in a general population: European Respiratory Society versus American Thoracic Society definition. Chest 2000;117: Suppl. 2 339S–345S.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]
- Celli BR, Halbert RJ, Isonaka S, Schau B. Population impact of different definitions of airway obstruction. Eur Respir J 2003;22:268–273.
[Abstract/Free Full Text] - Pellegrino R, Viegi G, Brusasco V, et al. Interpretative strategies for lung function tests. Eur Respir J 2005;26:948–968.
[Free Full Text] - Mannino DM. Defining chronic obstructive pulmonary disease ... and the elephant in the room. Eur Respir J 2007;30:189–190.
[Free Full Text] - Mannino DM, Buist AS, Petty TL, Enright PL, Redd SC. Lung function and mortality in the United States: data from the First National Health and Nutrition Examination Survey follow up study. Thorax 2003;58:388–393.
[Abstract/Free Full Text]
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