Back to top


Spirometry allows you to diagnose asthma, assess asthma control and severity.

It measures the degree of airflow limitation compared with predicted normal airflow and the reversibility of this limitation following bronchodilator therapy.


Clearly physically demonstrate to the patient what to do

  1. Sit upright with feet firmly on the floor, or stand if more comfortable for patient

  2. Breathe in until lungs feel absolutely full

  3. Form a good seal around the mouthpiece

  4. Blast out air as hard and fast as possible and for as long as possible, until the lungs are completely empty – aim for exhalation at maximal force for at least 3 seconds to provide a good measurement (a 6 second expiration is ideal)

Repeat until you obtain three reproducible and acceptable measures:

  • Forced expiration started immediately after full inspiration

  • Manoeuvre performed with a rapid expiratory start

  • Forced expiration must be maintained throughout the test

  • No coughing during first second of the test

  • The difference between the highest and second-highest values for FEV1 and FVC

Reversible airflow limitation is characterised by an increase in FEV1 by at least 12% and an increase in absolute FEV1 by 200mL compared to baseline.

Further resources

This YouTube video (7 minutes) produced by students at Oxford University Medical School in conjunction with the faculty demonstrates how to perform the basic lung function tests of spirometry and peak flow.

© Agency for Clinical Innovation 2023