How to perform peak flow and spirometry tests

Peak expiratory flow (PEF) and spirometry are the two most commonly used lung function tests in the diagnosis and monitoring of respiratory conditions. Both tests measure the speed and efficiency with which air moves in and out of the lungs. Conditions affecting airflow are called airway diseases and include asthma, chronic obstructive pulmonary disease (COPD), and bronchiectasis (including cystic fibrosis).

It is important that all junior doctors have a basic understanding of how and when to perform these tests and how to interpret the results. Before you do either test you must take a thorough medical history, conduct a full respiratory examination, and establish a differential diagnosis. Where respiratory disease is suspected, lung function tests can be used to confirm or refute the suspected diagnosis. Unlike many common medical tests, such as measuring blood sugar or blood pressure, normal lung function varies dramatically from person to person. In both tests the results vary, depending on the individual’s age, sex, and height. Consequently, the number recorded is expressed as a percentage of the expected or predicted value.