When Your Child Needs Pulmonary Function Tests

Pulmonary function tests can help tell how well your child’s lungs are working or how well the lungs are responding to medicine. These noninvasive, painless tests are done starting at around age 5 or 6. Your child may have one or more of these tests. The tests may last up to an hour.

Before the tests

Tell the healthcare provider if your child:

Is taking any medicines, including inhalers
Is allergic to latex, tape, or any medicines
Has had any recent illnesses, such as a chest cold or bronchitis

Help your child do the following to get ready:

Stop any medicines as directed by the healthcare provider.
Follow any directions from the provider for not eating or drinking before or after the test.
Wear loose clothes that won’t restrict breathing.
Follow any other instructions you are given.

During spirometry

This test measures the volume of air your child’s lungs can hold and how fast your child can breathe out (exhale) after taking in a big breath. It's the most common pulmonary function test for children. It takes about 10 to 15 minutes. During the test:

Your child puts their mouth around a mouthpiece on a long tube. This tube is attached to a computer.
A clip on the child’s nose prevents air from leaking out.
Your child breathes out through the mouthpiece, then takes in the biggest breath possible.
Your child blows out this big breath as hard, fast, and long as possible.

To confirm a diagnosis of asthma, the test may be repeated after your child is given a medicine called a bronchodilator.

During diffusion

This test measures how fast carbon monoxide moves from the lungs into the blood. Your child breathes in a very tiny bit of carbon monoxide briefly from a container. The amount of carbon monoxide used is not harmful. Your child then exhales the carbon monoxide. Its concentration is measured. The difference between what is inhaled and what is exhaled helps tell how well gas moves out of the lungs. During the test:

Your child puts their mouth around a mouthpiece.
A clip on the nose prevents air from leaking out.
Your child breathes through the mouthpiece, then exhales as much as possible.
Your child takes the deepest breath possible and holds for 10 seconds.
Your child breathes out. This air is analyzed.

During total lung capacity

This test lets the healthcare provider calculate the total amount of air your child’s lungs can hold. It measures the pressure changes while your child is breathing. During the test:

Your child goes into a clear booth called “the box.”
Your child sits inside and breathes into a long tube.
While your child breathes, a computer calculates the amount of air in the child’s lungs.

During pulse oximetry

This test measures the level of oxygen in the blood. During the test:

A small, painless clip is put onto a finger, earlobe, or toe.
This clip is attached to the pulse oximeter by a cable. The oximeter is a small machine that measures oxygen levels.
The clip is removed after a short time.

After pulmonary function tests

Your child can return to normal life right away. Ask your child’s healthcare provider about when and how to return to any medicines that were stopped for the tests. You can expect test results in a few days.

Helping your child get ready

You can help your child have a more positive experience by preparing them in advance. How you do this depends on your child’s needs.

Explain the tests to your child in short and simple terms. For lung capacity testing, be sure to describe “the box” to your child. It will help to see it in advance, if possible.
Younger children tend to have shorter attention spans. So any preparation should take place shortly before a test. Older children should be given more time to understand the test in advance.
Have your child practice blowing on party favors or pinwheels to help get ready for the sustained breaths needed during these tests.
Make sure your child understands which body parts will be involved.
Describe how the tests will feel as best you can. Also prepare your child for what to expect afterward. Let your child ask questions.
Use play when appropriate, such as for school-age children. This can include role-playing with a child’s favorite toy or object. Older children may want to see pictures or films that show them clearly what will happen during the test.