Lung function tests

Lung function tests measure the air you breathe in and out, to assess how well your lungs are working. Find out more about these quick and easy, yet vital tests. 

2 min read

A patient receiving a lung function test

Lung function tests help to identify the early signs of lung problems or track their progression.1

There are two main tests your doctor/nurse will be interested in:

1. Spirometry 

Looking at:

How much air is going into your lungs and how quickly air is inhaled and exhaled. The measurements will be made by a machine called a spirometer.

What to expect:

You will be required to breathe into a tube in different ways. This will enable the doctor or nurse to take measurements, such as:

  • Forced vital capacity (FVC). ​The total amount of air that can be breathed out in one breath (breathing ability).2,3

  • Forced expiratory volume in 1 second (FEV1). The amount of air that can be blown out quickly, in 1 second.2,3



Understanding your results:

Lung fibrosis (scarring) can reduce the capacity and flexibility of your lungs, and can change how you breathe. Fibrosis, or scarring, can make your lungs 'stiff'.4 So the amount of air you can breathe in is reduced because your lungs are unable to fully expand.4

Your results on this test can be compared against what would be expected for someone of your age, height, race and sex. They can also be compared with your previous measurements, so that your progress can be tracked over time. 

2. Diffusing capacity of the lungs for carbon monoxide (DLCO)

Looking at:

How much of the air you breathe in is exchanged with your blood (gas exchange).5

What to expect:

DLCO is calculated by using a carbon monoxide (CO) diffusion capacity test. The doctor/nurse will ask you to breathe in a small amount of air. You then hold your breath for 10 seconds before rapidly blowing the air out. 

Understanding your results:

This test tells the doctor/nurse how much of the air you breathe in is exchanged with your blood. It gives a percentage that can help to predict problems in the future.

If the tiny air sacs (alveoli) in your lungs are inflamed or thickened by fibrosis, gases won’t be able to go in/out of the blood so easily.5 Gas exchange is also affected if there are problems with the blood vessels in your lungs, like with PAH.