Lung function tests

This page explains about lung function tests and what to expect when your child comes to Great Ormond Street Hospital (GOSH) to have this procedure.

What is a lung function test?

Lung function tests are performed by respiratory physiologists within a dedicated lung function laboratory.

A lung function test aims to evaluate how well the lungs are working. The most commonly performed tests are used to measure lung volumes, airway functioning and the efficiency of gas exchange.

These tests allow us to take baseline measurements and monitor lung function over time. They will assist the medical team throughout the child’s care and can be performed from the age of around three to four years.

We aim to make lung function tests fun and enjoyable for the child by creating a comforting environment. 

What happens before the test?

If the test is being performed as an outpatient you will receive an appointment letter in the post. If your child is having a lung function test as an inpatient, the ward will arrange it and let you know when the appointment will take place. The medical team who request the test will explain in detail the requirement of the test and answer any questions.

When you arrive at the lung function lab, you and your child will be greeted by a clinical physiologist. The physiologist will explain the test and will be happy to answer any questions. Prior to the test we will measure your child’s height and weight. 

What do the tests involve?

The lung function laboratory has a number of machines designed to test different aspects of your child’s lung function. Below is a brief description of some of the tests your child may perform: 

Jayden with physio
Spirometry test in GOSH lung function laboratory


This test looks at how fast you can blow air out through the airways. This allows us to measure the flow of air from your lungs. Your child will be asked to breathe in until their lungs are completely filled with air before blowing out as hard and as fast as they can through a mouthpiece into a measuring device.

Lung volumes

For this test your child will sit inside a cubicle that looks similar to a telephone box. During the time in the box your child will perform a range of breathing exercises, which will allow us to calculate the volume of air in the lungs.

Gas transfer

This test measures how easily oxygen is transferred across the lung and into the blood. Your child will be asked to breathe in one very big breath of a harmless gas, and hold it in their lungs for about ten seconds before blowing it out again.

We also perform basic exercise tests and other, more specialised, tests when required.

The tests rely on patient effort, so we will give your child plenty of encouragement to help them to achieve reliable results. We have a range of games and incentives built into the testing programmes to make the test enjoyable and easy for your child.

How long does the test last?

The testing can last from between 15 to 90 minutes, depending on the number of different tests that are required. Your appointment letter will give an approximate duration of the test. We try to maintain your child’s interest throughout testing by making the experience as enjoyable as possible and allowing time to rest between tests.

How long until we get the results?

If you have an appointment to see the doctor on the same day as the test, a copy of the results will be given to you. If you are not seeing the doctor on the day of your test, we will send a report so it is available for your next appointment. At this time the doctor will be able to explain the results to you.

Compiled by: 
Great Ormond Street Hospital
Last review date: 
June 2016


Please note this is a generic GOSH information sheet. If you have specific questions about how this relates to your child, please ask your doctor. Please note this information may not necessarily reflect treatment at other hospitals.