Health Library
Pulmonary Function Test: Diffusion Test

What Is a Diffusion Test?

The Division of Pulmonary Medicine at Cincinnati Children's performs diffusion tests.

Diffusion tests measure gas transfer from the lungs into the bloodstream. Various diseases can cause changes in the lungs and affect this measurement.

How Is the Test Done?

Diffusion is measured by having your child place padded nose clips on his or her nose and placing their mouth around a single use, disposable, filtered mouthpiece. The mouthpiece is connected to a computer.

Your child will be instructed to breathe normally, exhale fully, take a large quick breath in of a mixture of gases, hold for 10 seconds and then fully exhale. The test can be repeated up to five times with a break in-between trials.

How Long Does It Take?

Like all pulmonary testing, diffusion tests are patient effort dependent and are performed along with other tests. These tests could take up to one hour.

How Does My Child Prepare?

Avoid the following activities:

  • Smoking 24 hours before the test
  • Exercising within one hour of testing
  • Eating two hours before testing

Are There Side Effects?

There are no side effects from diffusion testing, and your child may resume normal activities after testing.

The mixture of gases includes a small amount of carbon monoxide that is safe for children of any age.

Last Updated 06/2022

Reviewed By Anna Baumer, RRT