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Quantifying severity of airway obstruction in COPD

The European Respiratory Society, British Thoracic Society and American Thoracic Society (see international recommendations) have recommended to use the FEV1/(F)VC ratio to decide whether there is or is not airway obstruction, and to quantify its severity on the basis of the FEV1.  In spite of ethnic differences in FEV1 and (F)VC, the FEV1/(F)VC ratio differs little, if at all, between ethnic groups, from childhood to old age. This was recently corroborated in the large multi-ethnic study carried out by the Global Lung Function Initiative. Therefore, FEV1/FVC offers a robust solution to diagnosing airway obstruction independent of ethnic or sex-related differences in ventilatory function. The world is divided as to what constitutes airway obstruction: according to the GOLD group an FEV1/FVC ratio < 0.70, but according to common sense, scientific rigor and clinical evidence the appropriate lower limit of normal is the 5th percentile.

The level of FEV1 is used to grade severity of airways obstruction; this is fraught with difficulties:

In keeping with international recommendations the severity of airway obstruction is based on the level of FEV1%predicted. Recommendations on the scaling of severity varied in time and between respiratory societies.

FEV1%FVC post bronchodilator FEV1%pred ATS/ERS 2004 GOLD NICE 2010
< 0.70 >80 mild mild (1) mild (1) *
< 0.70 50-79 moderate moderate (2) moderate (2)
< 0.70 30-49 severe severe (3) severe (3)
< 0.70 < 30 very severe very severe (4) very severe (4)
        * diagnosis of COPD requires the presence of respiratory symptoms

FEV1%FVC FEV1%pred ATS/ERS 2005
< LLN >70 mild
< LLN 60-69 moderate
< LLN 50-59 moderately severe
< LLN 35-49 severe
< LLN < 35 very severe

As argued earlier, the use of percent of predicted is misguided because it leads to age-related bias, due to which the severity of airway obstruction will be systematically overestimated in elderly people. Only an FEV1/FVC ratio < LLN and FEV1 < LLN was found to be associated with elevated risk of having respiratory symptoms and elevated risk of death (PubMed); therefore it would be better to abandon using FEV1 % predicted and adopting the LLN for FEV1 in defining mild airway obstruction.

International recommendations
1 ATS statement. Standards for the diagnosis and care of patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 1995; 152: S77-S120.
2 ERS consensus statement. Optimal assessment and management of chronic obstructive pulmonary disease (COPD). Siafakas NM, Vermeire P, Pride NB, Paoletti P, Gibson J, Howard P, Yernault JC, Decramer M, Higenbottam T, Postma DS, Rees J, and Task Force. Eur Respir J 1995; 8: 1398-1420. PubMed
3 BTS. COPD guidelines. Thorax 1997; 52 suppl. 5: S1-S28. PubMed
4 National Institute for Clinical Excellence. Clinical Guideline 101. Chronic obstructive pulmonary disease, October 2010. PubMed
5 ATS/ERS Task Force: Standards for the diagnosis and treatment of patients with COPD: a summary of the ATS/ERS position paper. Eur Respir J 2004; 23: 932–946. PubMed
6 Pellegrino R, Viegi G, Brusasco V, et al. Interpretative strategies for lung function tests. Series "ATS/ERS Task Force: Standardisation of Lung Function Testing". Eur Respir J 2005; 26: 948-968. PubMed
7 CG101 Chronic obstructive pulmonary disease (October 2010): NICE guideline. PubMed
8 Quanjer PH, Stanojevic S, Cole TJ et al. and the ERS Global Lung Function Initiative. Multi-ethnic reference values for spirometry for the 3-95 years age range: the Global Lung Function 2012 equations. Eur Respir J 2012; 40: 1324–1343. PubMed

Ethnic differences in FEV1%FVC

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28 Quanjer PH, Stanojevic S, Cole TJ et al. and the ERS Global Lung Function Initiative. Multi-ethnic reference values for spirometry for the 3-95 years age range: the Global Lung Function 2012 equations. Eur Respir J 2012; 40: 1324–1343.

FEV1 underestimated

  Van der Molen T. Asthma treatment in general practice. Academic thesis, Groningen, 1997. ISBN 90 3670786 2.

Use the lower limit of normal for the FEV1/FVC ratio to define airway obstruction

1 Ekberg-Aronsson M, Pehrsson K, Nilsson JA, Nilsson PM, Löfdahl CG. Mortality in GOLD stages of COPD and its dependence on symptoms of chronic bronchitis. Respiratory Research 2005, 6: 98. PubMed
2 Vaz Fragoso CA, Concato J, McAvay G, Van Ness PH, Rochester CL, Yaggi HK, Gill TM. Chronic obstructive pulmonary disease in older persons: A comparison of two spirometric definitions. Respir Med. 2010; 104: 1189-1196. PubMed
3 Pedone C, Scarlata S, Sorino C, Forastiere F, Bellia V, Antonelli Incalzi R. Does mild COPD affect prognosis in the elderly? BMC Pulm Med. 2010; 10: 35. PubMed
4 Mannino DM, Doherty DE, Sonia Buist A. Global Initiative on Obstructive Lung Disease (GOLD) classification of lung disease and mortality: findings from the Atherosclerosis Risk in Communities (ARIC) study. Respir Med. 2006; 100: 115-122. Pubmed
5 Bridevaux PO, Gerbase MW, Probst-Hensch NM, Schindler C, Gaspoz JM, Rochat T. Long-term decline in lung function, utilisation of care and quality of life in modified GOLD stage 1 COPD. Thorax 2008;63 : 768-174. PubMed
6 Mannino DM, Buist AS, Vollmer WM. Chronic obstructive pulmonary disease in the older adult: what defines abnormal lung function? Thorax 2007; 62: 237–241. PubMed
NOTE: Although the summary of the publication suggests otherwise, the authors misrepresented their findings: the adjusted hazard ratio for premature death was elevated only if the FEV1/FVC ratio was < LLN.
7 Vaz Fragoso CA, Concato J, McAvay G, Van Ness PH, Rochester CL, Yaggi HK, Gill TM. The ratio of FEV1 to FVC as a basis for establishing chronic obstructive pulmonary disease. Am J Respir Crit Care Med 2010; 181: 446-451. PubMed
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