Spirometry
A breathing test measuring how much air you can blow out, and how quickly.
What it means
Spirometry measures lung function by recording a forced breath out into a machine. Two numbers matter most:
- FEV1 — the volume blown out in the first second
- FVC — the total volume blown out
Their ratio separates two patterns. An obstructive pattern (reduced FEV1/FVC) means airflow is limited — asthma or COPD. A restrictive pattern (both reduced, ratio preserved) means the lungs cannot expand fully — fibrosis, obesity, chest wall problems.
Reversibility testing — repeating after an inhaler — helps separate asthma, which reverses substantially, from COPD, which does not.
In practice
Results are given as a percentage of predicted values for age, height, sex and ethnicity.
Spirometry is required to diagnose COPD, and a diagnosis made without it is not secure. Peak flow is a simpler, cruder measurement used mainly to monitor asthma.
Why it matters
The test is effort-dependent and needs proper coaching — poor technique produces results that look like disease.
Anyone told they have COPD without ever having had spirometry should ask for it. Some are found to have asthma instead, which is treated differently and responds much better.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 30, 2026