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A peak flow (PEF) meter is a pocket-sized machine that measures peak expiratory flow (PEF). A person measures PEF by taking a deep breath and then breathing into a tube on the meter as hard and as fast as possible. PEF results depend on how hard you try.

The peak flow meter should be used 3 times and the best result recorded. Peak expiratory flow meter results are not as accurate as spirometry (done in a doctor's office), but both measure lung function.

People who use a home peak flow meter need to use the same meter over time because different brands of meters give different values for results. If you change meters, you need to determine your personal best measurement using the new machine.

Wash meters in soapy water every 2 weeks to prevent growth of bacteria and fungi.

Before testing, make sure you have no food or gum in your mouth. Follow these steps to use a peak flow meter:

1. Put the pointer on the gauge of the peak flow meter to 0.
2. Attach the mouthpiece to the peak flow meter.
3. Stand up and take a deep breath.
4. Put the peak flow meter mouthpiece in your mouth and close your lips tightly around the outside of the mouthpiece. Don't put your tongue inside the mouthpiece.
5. Breathe out as hard and as fast as you can, using a "huff" rather than a full breath out.
6. Record the value on the gauge in your asthma diary.
7. Move the pointer on the gauge back to 0 before you blow again.
8. Blow into the peak flow meter two more times. Record your values each time. If you cough or make a mistake during the testing, do the test over.
9. After you have blown into your peak flow meter three times, record the highest value on your daily record sheet.