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What is a pulmonary function test?

A pulmonary function test (PFT) is a set of diagnostic tests used to evaluate your child’s lung function or to measure any change in lung health. Pulmonary function testing is often used to diagnose and monitor chronic pulmonary conditions, such as asthma, cystic fibrosis, or bronchopulmonary dysplasia.

What are the different types of PFTs?

Pulmonary function testing may involve several different tests.


Spirometry is one of the most common types of pulmonary function tests and is performed by blowing into a plastic tube. The test measures how much air your child can exhale in a single breath and how fast the air comes out. It is especially helpful for determining whether there are any blockages in the airways that impair breathing.

Lung volumes

Lung volume tests measure the total amount of air your child’s lungs can hold. This test, too, involves breathing through a plastic tube. It can either be done sitting in an enclosed space that can measure pressure differences when taking a big breath or by breathing a mixture of air and a very small and completely safe amount of helium, and measuring the concentration of helium at various points in the process.

Diffusion capacity of the lungs

The diffusion capacity of the lungs refers to how easily oxygen can enter the body during regular breathing. The test is performed by having your child breathe into a tube with a very small, and completely safe, amount of carbon monoxide added.

Oxygen saturation

Another important and simple test measures the amount of oxygen in the blood. A device called a pulse oximeter beams a small red light on your child’s fingernail and measures how much light is absorbed. This reflects how much oxygen is in the blood without causing any discomfort.

Specialty pulmonary function tests

In addition to the most common PFTs described above, Boston Children’s pulmonary function testing lab performs several other specialty tests:

  • exercise tests, such as the six-minute walk test, the exercise saturation study, cardiopulmonary exercise tests, and exercise-induced asthma tests
  • high-altitude stimulation test (measuring oxygen levels as they would be in a pressurized airplane cabin)
  • measures of respiratory muscle strength (how much force the chest can generate to take a breath)
  • measurement of breathing in response to medications
  • measures of airway inflammation (how much nitric oxide, a gas produced in allergic inflammation, is present in exhaled air)

What should my child do to prepare for a pulmonary function test?

Pulmonary function tests do not cause discomfort. Some tests require your child to use maximal effort to breathe in and out. They will be repeated several times to make sure the results are accurate. A few things to keep in mind:

  • Avoid eating large meals before testing.
  • Wear loose clothing.
  • Continue daily medications unless instructed otherwise.
  • If possible, stop using short-acting bronchodilators (like albuterol or ipratropium) at least six hours before testing.

Are there risks to pulmonary function tests?

In general, pulmonary function testing is completely safe. For some tests, your child may feel dizzy or uncomfortable for a moment after testing because of breathing fast and hard. If you have concerns about how well your child may tolerate the specific test, please consult your care team or reach out to our pulmonary lab technicians.

There are certain situations in which we recommend not performing certain tests, such as if your child has recently coughed blood, has severe chest pain, had a recent pneumothorax (air leak outside the lungs), or has had recent oral, facial, eye, or sinus surgery. You should consult with your care team for guidance.

What happens after the pulmonary function test?

The results of your child’s pulmonary function tests will be reviewed by one of our pulmonary medicine specialists. The reports will be forwarded to your referring physician to help with your care plan.

How can I schedule a pulmonary function test?

A PFT can be scheduled by calling our Pulmonary Function Testing Lab at 617-355-7510. A referral from your child’s primary care provider may be required.

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