Lung Function Tests

Lung function tests are a group of tests that measure how well your lungs work.

What are lung function tests?
Why do I need a lung function test? 
What are the risks of lung function tests?
How do I prepare for lung function tests?
What happens during a lung function test?
What happens after a lung function test?

What are lung function tests?

Lung function tests check how well your lungs and airways work. These tests measure the amount of air you breathe in and out. Lung function tests are also known as pulmonary or respiratory function tests.

Why do I need a lung function test? 

Your doctor may order one or more lung function tests if you:

  • Already have a lung condition – your doctor may order lung function tests to check that your condition is improving and responding to treatment
  • Are exposed to certain substances (in your environment or at work) that are linked with lung diseases
  • Are noticing symptoms related to lung disease
  • Are preparing for surgery
  • Have a suspected lung condition.

Lung function tests can help diagnose the following diseases and conditions:

Below, you can watch a short video from one of our doctors explaining more about lung function tests.

 

 

Below, you can watch an animation explaining what happens during lung function tests.

What are the risks of lung function tests?

For most people, lung function tests are safe. However, tests that require you to breathe in and out quickly can cause dizziness. If you feel lightheaded during or after your tests, tell your scientist who is the person who performs the procedure.

If you have recently had a heart attack, surgery, a severe chest infection or heart disease, you may have an increased risk. Talk to your doctor to determine your risk.

How do I prepare for lung function tests?

If you’re taking medications, tell your doctor. Some medications can affect the test results, so you may need to stop taking your medicine temporarily. Be sure to tell your doctor about any over-the-counter medications and supplements you’re taking, too.

Your doctor will tell you what you to do to prepare. Here are some steps you will need to take on the day of your test:

  • Avoid caffeine – caffeine can open your airways which affects your test results    
  • Avoid strenuous exercise – don't exercise for at least an hour before your test    
  • Don’t eat a large meal – a full stomach can prevent your lungs from filling up
  • Keep your dentures in – wear them to the test to make sure your mouth can fit tightly around the mouthpiece.    
  • Stop smoking – don't smoke for at least an hour before your test
  • Wear loose clothing – tight clothing may restrict your breathing.

What happens during a lung function test?

Most lung function tests are straightforward and non-invasive. Still, every lung test requires you to put in the maximum effort to get accurate results. That means you may feel a bit tired and puffed, but not uncomfortable.

Here is some information about the different types of lung function tests.

Name of test

What does it measure?

When is it used?

What happens during the test?

 

Spirometry

The amount of air breathed in and out.

How much the airways have narrowed.

To diagnose common lung conditions, such as asthma and COPD.

You will need to wear a nose clip to keep you from breathing through your nose.

Your scientist will ask you to breathe in and out, deeply and quickly, for several seconds. You might need to breathe in a medication that opens your airways. You can watch the animation above to find out more.

Plethysmography 'Body Box'

The volume of gas in your lungs (total lung capacity).

The amount of air left when you breathe out as much as possible (residual capacity).

To determine if your symptoms are due to a restrictive or an obstructive disease.

Restrictive lung diseases make it hard for you to fully expand your lungs and fill them with air.

Obstructive lung diseases make it hard for you to exhale all the air out of your lungs.

You’ll sit in a small, airtight chamber that looks similar to a phone booth. You’ll also wear a nose clip to keep you from breathing through your nose.

Your scientist will ask you to breathe or pant against a shutter that opens and closes.

While the chamber is a tight space, you will be able to see outside at all times. You can watch the animation above to find out more.

Lung Diffusion Capacity

How easily the lungs transfer gas from inhaled air to red blood cells.

To determine the severity of lung conditions such as emphysema and pulmonary fibrosis.

You will use a mouthpiece and a nose clip to prevent you from breathing through your nostrils.

You will take a breath of air which contains a small and safe amount of carbon monoxide. You will need to hold this air for a count of 10 or so, then quickly exhale. The air that you exhale will be collected and analysed.

Capillary Blood Test

How much oxygen and carbon dioxide is in your blood.

How well your lungs are working and if they are exchanging oxygen and carbon dioxide efficiently.

This test can help to work out if you need oxygen therapy.

A small amount of cream will be put on your earlobe to increase the blood flow in this area. This cream makes your ear go red and feel a bit hot.

After the cream is applied, the blood vessels in your ear lobe will contain about the same amount of oxygen as blood taken from an artery.

After a few minutes, your scientist will take a blood sample by gently pricking your earlobe and catching the blood droplet that forms.

The blood sample will be analysed to see whether or not your body is getting enough oxygen and getting rid of enough carbon dioxide.

 

A full lung function test, which includes all of the tests above, takes approximately 90 minutes.

What happens after a lung function test?

If you usually have lung or breathing problems, you may feel tired after your lung function tests. You will be given a chance to rest after the tests are finished. 

Your doctor will make an appointment with you to talk to you about your test results and work out your next steps and treatment plan.