Spirometry is a way of assessing respiratory function. It can be performed using a handheld spirometer or undertaken in a formal lung function clinic. Before and after using an inhaled bronchodilator, the patient’s forced expiratory volume in one second (FEV1), forced vital capacity (FVC) and FEV1/FVC ratio are measured, as well as their peak expiratory flow. Note that this should not be performed when someone is acutely unwell as it will not provide accurate results for diagnosis.

Abnormal results can be divided into two patterns, with different causes for each:

• Obstructive – including asthma or COPD as the cause
• Restrictive – for example, conditions causing problems with chest wall movement or lung elasticity.

The results need to be reviewed and interpreted in the context of the person’s overall symptoms and history in order to support a diagnosis of COPD. Someone with an FEV1/FVC ratio of less than 0.7 would usually be classed as having an obstructive pattern. Diagnosis should also be considered in symptomatic individuals with normal spirometry.

Oral corticosteroids should not be used routinely for reversibility testing or to predict response to inhaled corticosteroids in individuals.