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How to Use Your Peak Flow Meter

A peak flow meter helps you check how well your asthma is controlled. Peak flow meters are most helpful for people with moderate or severe asthma.

This guide will tell you:

  • how to find your personal best peak flow number.
  • how to use your personal best number to set your peak flow zones.
  • how to take your peak flow.
  • when to take your peak flow to check your asthma each day.

Starting Out: Find Your Personal Best Peak Flow Number

It is important to find out your personal best peak flow number. Each person's asthma is different, so your personal best peak flow number may be different from another person's personal best number.

To find your personal best peak flow number, take your peak flow each day for two to three weeks. Your asthma should be under good control during this time. Take your peak flow as close to the times listed below as you can. (These times for taking your peak flow are only for finding your personal best peak flow. To check your asthma, each day you will take your peak flow in the morning.)

  • Between noon and 2:00 p.m. each day.
  • Each time you take your quick-relief medicine to relieve symptoms. Measure your peak flow after you take your medicine.
  • Any other time your doctor or asthma educator suggests.
image of person writing peak flow numbers in chart

Write down the number you get for each peak flow reading. The highest peak flow number you had during the two to three weeks is your personal best. Your personal best can change over time. Ask your doctor when to check for a new personal best.

Your Peak Flow Zones

Your peak flow zones are based on your personal best peak flow number. The zones will help you check your asthma and take the right actions to keep it controlled. The colors used with each zone come from the traffic light.

 Green Zone    (80-100 percent of your personal best) signals good control. Take your usual daily long-term-control medicines, if you take any. Keep taking these medicines even when you are in the yellow or red zones.

Yellow Zone (50-79 percent of your personal best) signals caution: your asthma is getting worse. Add quick relief medicines. You might need to increase other asthma medicines as directed by your doctor.

Red Zone(below 50 percent of your personal best) signals medical alert!. Add or increase quick-relief medicines and call your doctor now.

Ask your doctor to write an Asthma Action Plan for you that tells you:

  • The peak flow numbers for your green, yellow, and red zones. Mark the zones on your peak flow meter with colored tape or a marker.
  • The medicines you should take while in each peak flow zone.

How To Take Your Peak Flow

  1. Move the marker to the bottom of the numbered scale (zero).
    image of peak flow meter with marker in middle of scale  image of peak flow meter with marker moved to bottom of scale
  2. Stand up or sit up straight.
  3. Take a deep breath. Fill your lungs all the way.
  4. Hold your breath while you place the mouthpiece in your mouth, between your teeth. Close your lips around it. Do not put your tongue inside the hole.
  5. Blow out as hard and fast as you can. Your peak flow meter will measure how fast you can blow out air.
    image of child holding peak flow meter before blowing out breath  image of child blowing out breath into peak flow meter
  6. Write down the number you get. But if you cough or make a mistake, do not write down the number. Do it over again.
  7. Repeat steps one through six two more times. Write down the highest of the three numbers. This is your peak flow number. If blowing out hard causes coughing and smaller numbers each time, write down the first number and make a note in your diary about what happened and why you wrote this number down.
  8. Check to see which peak flow zone your peak flow number is in. Do the actions your doctor told you to do while in that zone.

Your doctor may ask you to write down your peak flow numbers each day. You can do this on a calendar or other paper. This will help you and your doctor see how your asthma is doing over time.

Checking Your Asthma: When To Use Your Peak Flow Meter
  • Every morning when you wake up, before you take medicine. Make this part of your routine.
  • When you are having asthma symptoms or an attack. Also after you take medicine for the attack. This can tell you how bad your asthma attack is and whether your medicine is working.
  • Any other time your doctor suggests.

If you use more than one peak flow meter (such as at home and at school), be sure that both meters are the same brand.

Bring to Each of Your Doctor's Visits
  • Your peak flow meter.
  • Your peak flow numbers if you have written them down each day.

Also, ask your doctor or asthma educator to check how you use your peak flow meter – just to be sure that you are doing it right.

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