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Asthma and the Peak Flow Meter


How Often Should I Check my Peak Flow?

Peak flow values are best if they are checked at the same time each day, preferably once in the morning and again at night.


How Do I Determine My "Personal Best" Peak Flow Number?

The "personal best" peak expiratory flow (PEF) is the highest peak flow number you or your child can achieve over a two to three week period when asthma is under good control. Good control means you feel good and do not have any asthma symptoms.

Your personal best PEF is important because it is the number to which all of your other peak flow readings will be compared. Your asthma action plan, developed along with your asthma doctor, is based on this number.

To find your personal best peak flow number, take peak flow readings:

  • Twice a day for two to three weeks when asthma is in good control
  • At the same time in the morning and in the early evening
  • As instructed by your doctor or asthma care provider

You should always use the same meter, and disregard any readings that are very different from the rest

Once you have determined your or your child's personal best PEF, work with your asthma care provider to determine at what point you should start taking quick-relief drugs to relieve an asthma attack or seek emergency medical attention. These are called your asthma peak flow zones. All of this information should be recorded in your personal asthma action plan.

Then, continue to take peak flow readings each morning. Daily readings will help you:

  • Recognize early drops in airflow
  • Know when your child's personal best improves naturally as he or she grows

If your PEF drops below 80% of your personal best, follow your asthma action plan and check PEF more frequently that day or as directed by your doctor. Seek immediate help before your asthma symptoms worsen.


WebMD Medical Reference

Reviewed by Melinda Ratini, DO, MS on July 10, 2012
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