Spirometry is a common test used to assess how well your lungs work by measuring how much air you inhale, how much you exhale and how quickly you exhale. It is a test that can help diagnose various lung conditions. Spirometry is used to diagnose asthma and chronic obstructive pulmonary disease (COPD). Spirometry is also used to monitor the severity of some other lung conditions, and their response to treatment.

A spirometer is the device that is used to make the measurements. It has a mouthpiece that you use to blow into the device. A doctor or nurse may ask you to blow or breathe into a spirometer if you have chest or lung symptoms. First you breathe in fully and then seal your lips around the mouthpiece of the spirometer. You then blow out as fast and as far as you can until your lungs are completely empty. This can take several seconds. You may also be asked to breathe in fully and then breathe out slowly as far as you can. A clip may be put on to your nose to make sure that no air escapes from your nose. The measurements may be repeated two or three times to check that the readings are much the same each time you blow into the machine.

Why spirometry is carried out?

Spirometry can be used to help diagnose a lung condition if you have symptoms of a problem, or your doctor feels you're at an increased risk of developing a particular lung condition. For example, it may be recommended if you have a persistent cough or breathlessness, or if you're over 35 and smoke.

Conditions that can be picked up and monitored using spirometry include:

  • Asthma – a long-term condition in which the airways become periodically inflamed (swollen) and narrowed
  • Chronic obstructive pulmonary disease (COPD) – a group of lung conditions where the airways become narrowed
  • Cystic fibrosis – a genetic condition in which the lungs and digestive system become clogged with thick, sticky mucus
  • Pulmonary fibrosis – scarring of the lungs.

If you've already been diagnosed with one of these conditions, spirometry may be carried out to check the severity of the condition or see how you're responding to treatment.

Preparing for the test:

You'll be told about anything you need to do to prepare for the test. You should also avoid smoking for 24 hours before the test, and avoid strenuous exercise or eating large meals for a few hours beforehand. It's best to wear loose, comfortable clothing on the day of the test.

What happens during a spirometry test:

You'll be seated during the test and a soft clip will be placed on your nose to stop air escaping from it. The tester will explain what you need to do and you may be asked to have a few practice attempts first.

When you're ready for the test, you'll be asked to:

  • Inhale fully, so your lungs are completely filled with air
  • Close your lips tightly around the mouthpiece
  • Exhale as quickly and forcefully as you can

This will normally need to be repeated at least three times to ensure a reliable result. In some cases, the test may need to be repeated around 15 minutes after taking some inhaled bronchodilator medication. This can show if you have a lung condition that responds to these medications. Overall, your appointment should last around 30-90 minutes. You'll be able to go home soon after the tests have finished and can return to your normal activities.

Are there any risks or side effects:

Spirometry is a straightforward test and is generally considered very safe. Some people may feel dizzy, faint, shaky, sick or tired for a short period afterwards. Most people are able to have a spirometry test safely without any discomfort.