Measuring peak expiratory flow in adults with asthma

There is no single diagnostic test for asthma, but measurement of peak expiratory flow (PEF) plays an important role in the diagnosis and management of the condition (British Thoracic Society and Scottish Intercollegiate Guidelines Network (BTS and SIGN), 2016; National Institute for Health and Care Excellence (NICE), 2017).

PEF is an objective test to measure lung function and to support the assessment of airway obstruction or inflammation. It is recorded using a peak flow meter. Readings will vary from person to person, and will depend on factors such as height and age and on how constricted the patient's airways are. Figure 1 illustrates the effect that asthma has on the airway.

The PEF rate is defined as the highest flow achieved on forced expiration from a position of maximum lung inflation and is expressed in litres per minute (Dougherty et al, 2015). It will indicate how narrow or open the airways are.