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Lung Function Tests: About Your Child's Tests

What are these tests?

Lung function tests measure how much air your child's lungs hold and how quickly your child's lungs can move the air in and out. Spirometry is often the first lung function test that is done. Your child may also have other tests. These tests include gas diffusion tests, body plethysmography, inhalation challenge tests, and exercise stress tests. Your doctor will explain which tests your child needs.

These tests check how well your child's lungs work. They may also be called pulmonary function tests, or PFTs.

Why are these tests done?

Doctors use lung function tests to find the cause of breathing problems. These tests are used to diagnose lung diseases like asthma. Your child may have lung function tests before he or she has surgery. Or your doctor may use these tests to find out how well treatment for a lung problem is working.

How can you prepare for these tests?

  • Tell your doctor if your child has any other medical problems.
  • Tell your doctor if your child is allergic to any medicines.
  • Let your doctor know if your child takes medicines for a lung problem. Your child may need to stop some of them before the tests.

What else should you know before the tests?

  • Have your child wear loose clothing that does not restrict breathing.
  • Don't let your child eat a large meal just before the test. A full stomach may keep your child's lungs from fully expanding.
  • For 6 hours before the test, do not let your child exercise hard.

What happens during these tests?

What happens during the test depends on the type of test your child has. A respiratory therapist or technician will do the lung function tests.

For most tests, your child will wear a nose clip. This is to make sure that no air passes in or out of your child's nose during the test. Your child then breathes into a mouthpiece attached to a recording device.

  • For some tests, your child breathes in and out as deeply and quickly as he or she can.
  • Your child may repeat some tests after he or she inhales a medicine that expands the airways.
  • Your child may breathe certain gases, such as 100% oxygen or a mixture of helium and air.
  • For body plethysmography, your child sits inside a small booth with windows. The booth measures pressure changes that occur as your child breathes.

The therapist may urge your child to breathe deeply during some of the tests to get the best results.

Your child may have a blood test to check oxygen and carbon dioxide levels in the blood before, during, or after the lung function tests.

How long do these tests take?

The testing may take from 5 to 30 minutes. This depends on how many tests your child has.

What happens after these tests?

  • You will probably be able to take your child home right after the tests.
  • Your child can go back to his or her normal activities right away.

Follow-up care is a key part of your child's treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse call line if your child is having problems. It's also a good idea to know your child's test results and keep a list of the medicines your child takes.

Where can you learn more?

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