Spirometry is a common breathing test that measures how much air you can breathe out and how quickly. Doctors use it to help diagnose and monitor conditions such as asthma and COPD, and to see how well treatment is working.

What the test measures

You take a deep breath in and blow out as hard and as fast as possible into a mouthpiece connected to a machine. Two main values are recorded: the total amount of air you can blow out, and how much of that comes out in the first second. The pattern between them helps show whether airways are narrowed or lung volume is reduced.

Why it is useful

  • Helping to confirm or exclude airflow obstruction in people with cough or breathlessness
  • Telling asthma-type patterns from COPD-type patterns, together with the rest of the assessment
  • Monitoring lung function over time and the response to treatment
  • Assessing lung health in people with long-term smoke or dust exposure

How to prepare

  • Ask in advance whether to take or hold your inhalers before the test, and follow that advice.
  • Avoid smoking, and avoid heavy meals and strenuous exercise just before testing.
  • Wear comfortable clothing that does not restrict breathing.
  • Tell the technician about recent chest infections, surgery, chest or abdominal pain or any heart problems.

Understanding your results

Results are compared with expected values based on age, height, sex and other factors, and are interpreted together with your symptoms and examination — a single number does not make a diagnosis. Some people are asked to repeat the test after using a reliever inhaler to see whether airflow improves. Your doctor will explain what the report means for you.

Note: Whether spirometry is appropriate for you is a clinical decision made at consultation. Ask the clinic about availability before travelling.
Patient sources: NHLBI — COPD ↗ and NHLBI — Asthma ↗

Frequently asked questions

Is spirometry painful?

No. It involves breathing in fully and blowing out as hard and as long as you can into a mouthpiece. It can make you feel briefly lightheaded or tired.

Can spirometry diagnose asthma or COPD by itself?

It provides important evidence, but diagnosis also depends on your history, examination and sometimes repeat testing or other investigations.

This article is general education and does not replace an examination, diagnosis or treatment plan.