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Asthma: Using a Peak Flow Meter

What is a peak flow meter?

A peak flow meter is a device used to measure how well your asthma is under control.

Hand holding peak flow meter.

The device measures air flow out of the lungs (peak expiratory flow rate or PEFR), as you blow into it. When used correctly, a peak flow meter can show that you have narrowing of the airways before you have symptoms. Peak flow readings can help you know:

  • When to get emergency medical care

  • How well your asthma treatment plan is working

  • When to stop or add medicine, as directed by your healthcare provider

  • What triggers your asthma symptoms

What are peak flow zones?

Peak flow zones may be part of your Asthma Action Plan. If you don't have an Asthma Action Plan, or if yours isn't up-to-date, make sure you talk with your healthcare provider. The 3 zones tell you when your asthma is controlled, when it is getting worse, and when it is severe. They are based on the traffic light concept. Green means safe. Yellow means caution. Red means danger. Based on your personal best peak flow measurement (your best lung function), your 3 peak zones include:

  • Green. This is 80% to 100% of your personal best peak flow measurement. This means your asthma is under control.

  • Yellow. This is 50% to 79% of your personal best peak flow measurement. This is a sign that your asthma is getting worse. You may need to use quick-relief medicines or other medicine, as directed by your healthcare provider.

  • Red. This is below 50% of your personal best peak flow measurement. This is a medical emergency. You should take quick-relief medicine and get medical help right away.

Using peak flow zones helps you see when your asthma may start to become uncontrolled. The goal is to stay in the green zone. Zones with a smaller range, such as 90% to 100%, may be recommended by some healthcare providers.

The numbers for each of your peak flow levels should be marked on your meter. If you need help with this, ask your healthcare provider or nurse. Your provider will also note your usual symptoms and what you should do for each zone in your Asthma Action Plan. The steps could be such things as what medicine to take, when to call the healthcare provider, or when to go to the emergency room. 

How is a personal best peak flow measured?

Your peak flow zones are based on your personal best peak flow. To find your personal best peak flow, take your peak flow measurement each day at the same time in the middle of the day for 2 to 3 weeks, when your asthma is under control . Write down all of the readings. Your personal best is the highest number during this time. This number is important if your asthma provider has given you an Asthma Action Plan that uses your peak flow. 

Your personal best peak flow measurement may change over time. Talk with your healthcare provider about when you should recheck your personal best.

When should a peak flow meter be used?

Use your peak flow meter regularly to check how well your asthma is being controlled. Measure your peak flow:

  • Each morning, before taking asthma medicines

  • When you have symptoms or an asthma flare-up

  • After taking medicine for an asthma flare-up

  • Other times as advised by your healthcare provider

Talk with your healthcare provider about when and how often you should be checking your peak flow readings. Tell your provider your peak flow readings.

How do I use the peak flow meter?

  • Stand up or sit up straight

  • Place the marker at zero or the lowest number

  • Take a deep breath. Put the mouthpiece into your mouth and wrap your lips tightly around it. Don't block the mouthpiece with your tongue. Make sure you don't have anything in your mouth, like gum.

  • Blow out through the mouthpiece as hard and fast as you can in 1 breath

  • The breath should move the marker on the meter. Note the number.

  • Repeat this routine a total of 3times

  • Record the highest of the 3 readings

How can I get a peak flow meter?

Peak flow meters are available at most drugstores and pharmacies. Some healthcare providers may also have them in their offices. Make sure you read all directions that come with the meter. If you have any questions, ask your provider or nurse. The best way to know if you are using the meter correctly is to use it in front of your healthcare provider or a nurse.

Online Medical Reviewer: Dan Brennan MD
Online Medical Reviewer: Deborah Pedersen MD
Online Medical Reviewer: Jessica Gotwals RN BSN MPH
Date Last Reviewed: 5/1/2023
© 2000-2024 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.