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Lung Function Tests: About These Tests

What are these tests?

If you're having lung problems or trouble breathing, it's important to get your lungs tested. Ask your doctor about breathing tests (or lung function tests).

Lung function tests measure how much air your lungs hold and how quickly your lungs can move the air in and out. Spirometry is often the first lung function test that is done. You may also have other tests, such as gas diffusion tests, lung volume testing, inhalation (or methacholine) challenge tests, and exercise stress tests. Your doctor will explain which tests you need.

These tests check how well your lungs work. They may also be called pulmonary function tests, or PFTs. A complete or full PFT usually involves most of the types of tests listed above, but a full PFT is not always necessary. For example, only the spirometry test is necessary to diagnose asthma or COPD.

Sometimes other tests are done at the same time as the lung function tests. For example, you may have a blood test to check the oxygen and carbon dioxide levels in your blood (arterial blood gas test or ABG). Or you may have a small sensor attached to your finger to check the oxygen level in your blood (oximetry).

Why are these tests done?

Doctors use lung function tests to see if your breathing problems are caused by lung disease and diagnose lung diseases like asthma or COPD (chronic obstructive pulmonary disease). You may have lung function tests before you have surgery. Or your doctor may use lung function tests to find out how well treatment for a lung problem is working.

How do you prepare for these tests?

  • Let your doctor know if you take medicines for a lung problem. You may need to stop some of them before the tests. You will get instructions about the test and what you need to do before coming for your appointment. It’s important to follow these instructions carefully. If you’ve been asked to stop medicines but you took them, you may be asked to rebook the test for another day.
  • Do not eat a heavy meal just before this test. A full stomach may keep your lungs from fully expanding.
  • Don't smoke, vape, or do intense exercise for 6 hours before the test.
  • For the test, wear loose clothing that doesn't restrict your breathing in any way.
  • Avoid food or drinks with caffeine. Caffeine can cause your airways to relax and allow more air than usual to pass through.
  • If you have dentures, wear them during the test, if they fit comfortably. They help you form a tight seal around the mouthpiece of the machine.

How are these tests done?

For most tests, you will wear a nose clip. This is to make sure that no air passes in or out of your nose during the test. You then breathe into a mouthpiece attached to a recording device.

  • For some tests, you breathe in and out as deeply and as fast as you can.
  • You may repeat some tests after you inhale a medicine that expands your airways.
  • For gas diffusion or lung volume testing, you sit inside a glass booth with big windows all around.

The healthcare professional will coach you and may ask you to breathe deeply during some of the tests to get the best results.

How long do these tests take?

The testing may take from 15 to 60 minutes, depending on how many tests you have.

What happens after these tests?

  • You can go back to your normal activities right away.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse advice line (811 in most provinces and territories) if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.

Where can you learn more?

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