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Lung Disease & Respiratory Health Center

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Home Lung Function Test

How It Is Done

Before you begin to test your peak expiratory flow (PEF), remove any gum or food you may have in your mouth. Follow these steps to use your peak flow meter:

  1. Set the pointer on the gauge of the peak flow meter to 0 (zero).
  2. Attach the mouthpiece to the peak flow meter.
  3. Stand up to allow yourself to take a deep breath. Make sure you use the same position each time you test your PEF.
  4. Take a deep breath in. Place the peak flow meter mouthpiece in your mouth and close your lips tightly around the outside of the mouthpiece. Do not put your tongue inside the mouthpiece.
  5. Breathe out as hard and as fast as you can using a huff. You do not need to breathe out for more than a second.
  6. Note the value on the gauge.
  7. Move the pointer on the gauge back to 0 (zero) before you blow again.
  8. Blow into the peak flow meter 2 more times. Record your values each time you blow. If you cough or make a mistake during the testing, do the test over.
  9. After you have blown into your peak flow meter 3 times, record the highest value on your daily record sheet.

How It Feels

Breathing in and out very quickly during these tests may make you feel lightheaded or may make you cough. If you feel like you are going to pass out, stop the test.


There are no significant risks linked with measuring peak expiratory flow (PEF). Breathing in and out very quickly during the test may make you feel lightheaded or may make you cough. If you feel lightheaded, stop the test.


A home lung function test uses a peak flow meter camera.gif or a home spirometer to monitor and evaluate any breathing problems you may have on a day-to-day basis. A peak flow meter allows you to measure your peak expiratory flow (PEF). PEF measures how much air you breathe out when you try your hardest. A home spirometer allows you to measure your forced expiratory volume at 1 second (FEV1). Results from these tests can be compared to monitor the progression of disease or help measure your response to medical treatment for a long-term (chronic) lung disease, such as asthma.

Peak flows are compared to charts that list normal values based on age, sex, race, and height. They also can be compared with your personal best measurement. Check with your doctor or read the information included with your peak flow meter to find your normal range, which will vary depending on the type of breathing problems you may have. If you find abnormal results on any of the tests, discuss them with your doctor.

  • Normally, peak flows vary slightly throughout the day. They are usually lower in the morning and higher in the afternoon.
  • A person with poorly controlled asthma may have peak flows that vary more widely throughout the day.

WebMD Medical Reference from Healthwise

Last Updated: September 09, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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