C2.3 Spirometry

The diagnosis of COPD rests on the demonstration of airflow limitation which is not fully reversible (NHLBI/WHO Workshop Report, April 2001) [evidence level II]

Because COPD is defined by a post-bronchodilator FEV₁/FVC ratio < 0.7, spirometry is essential for its diagnosis (see Box 5). Most spirometers provide predicted (“normal”) values obtained from healthy population studies, and derived from formulas based on height, age, sex and ethnicity.

Airflow limitation is not fully-reversible when, after adminis­tration of bronchodilator medication, the ratio of FEV₁ to forced vital capacity (FVC) is <70% and the FEV₁ is <80% of the predicted value. The ratio of FEV₁ to vital capacity (VC) is a sensitive indicator for mild COPD.

A detailed systematic review states that spirometry, in addition to clinical examination, improves the diagnostic accuracy of COPD compared to clinical examination alone reinforcing the importance of spirometry (Wilt et al., 2005) (evidence level I). More studies are required to define any benefit from the use of spirometry for case finding in COPD, and to evaluate the effects of spirometric results on smoking cessation.

The spirometric tests require high levels of patient effort and cooperation, and there are important quality criteria that should be met in conducting spirometry.(Miller et al., 2005)

Indications for spirometry include:

• breathlessness that seems inappropriate;
• chronic (daily for two months) or intermittent, unusual cough;
• frequent or unusual sputum production;
• relapsing acute infective bronchitis; and
• risk factors such as exposure to tobacco smoke, occupa­tional dusts and chemicals, and a strong family history of COPD.