Spirometry
Also known as: breathing test, lung function test
A forced breath out into a tube measures how much air the lungs can move and how fast. It is the test that diagnoses and grades asthma and COPD by separating airways that are narrowed (obstruction) from lungs that are stiff or small (restriction).
- Abbreviations
- FEV1, FVC
- Kind
- Physiological or functional test
- Categories
- Respiratory
- Specimen
- No specimen
- Method
- Spirometry
What it measures
| Measure | What it tells you |
|---|---|
| FEV1 | The volume blown out in the first second; reduced when airways are narrowed. |
| FVC | Forced vital capacity, the total volume blown out; reduced when lungs are small or stiff. |
| FEV1/FVC ratio | Below 0.7 defines airflow obstruction (asthma, COPD). |
| Reversibility | FEV1 improving by 12% and 200 mL after a bronchodilator suggests asthma rather than COPD. |
| Peak expiratory flow | The fastest flow, measured at home on a hand-held meter to track asthma control. |
Why it is ordered
- Breathlessness, wheeze or chronic cough
- Smokers over 35 with symptoms (COPD screening)
- Asthma diagnosis and monitoring
- Before lung or major surgery
- Occupational lung disease surveillance
How it is done
Take the deepest breath possible and blast it out as hard and long as possible through a mouthpiece, repeated three times; 15-30 minutes with a bronchodilator test.
Preparation. Avoid inhalers, big meals, alcohol and vigorous exercise before the test as instructed.
Reading the result
| Finding | Usual meaning |
|---|---|
| FEV1/FVC below 0.7, poor reversibility | COPD; severity graded by FEV1 as % predicted |
| Obstruction that reverses with salbutamol | Asthma |
| Low FVC with normal ratio | Restrictive pattern: fibrosis, chest wall or muscle disease, obesity; full lung function tests next |
Reference ranges vary by laboratory, method, age, sex and clinical context; a result is read against the person, not a table.
Limitations
Depends on effort and technique; normal spirometry between attacks does not exclude asthma. Not safe soon after a heart attack, eye surgery or pneumothorax.
Catalogued concepts this page covers
Concepts of the master test taxonomy that resolve to this page; each links to its category.