Quantifying the 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 (LLN) is the 5th percentile. The decision about choosing criterion has a very strong impact, especially in older patients, where real LLNis much lower than 0.7. It is well known phenomenon, that using 0.7 as a cut-off point lead to substantial overdiagnosis of COPD in general population and as comorbidity (eg. in heart failure patients).

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

The recommendations relate to COPD and do not take account of coexisting restrictive ventilatory defects.
Restrictive lung disease associated with an FEV1/(F)VC ratio below a borderline leads to overestimating the severity of airway obstruction.
Each assessment is very sensitive to how well the reference values used fit the population.
General practitioners tend to underestimate FEV1 by up to 280 mL, depending on equipment used and previous training (see FEV1 underestimated). In general this is to be expected if spirometric measurements are not performed by professionally trained personnel and do not conform to international recommendations. If FEV1/(F)VC is below ‘normal limits’, airway obstruction then tends to be systematically overestimated when based on the level of FEV1.
FEV1 expressed as %predicted compares value to the mean in population but relative reduction may be effect of the poor lung growth and not associated with the disease

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
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4	National Institute for Clinical Excellence. Clinical Guideline 101. Chronic obstructive pulmonary disease, October 2010. PubMed
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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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FEV1 underestimated
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Use the lower limit of normal for the FEV1/FVC ratio to define airway obstruction
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Last modified on 03.12.2018 15:21