What is peak flow measurement?

Peak flow measurement is a quick test to measure air flow out of the lungs. The measurement is also called the peak expiratory flow rate (PEFR) or the peak expiratory flow (PEF). Peak flow measurement is mostly done by people who have asthma or a long-term (chronic) lung disease.

Peak flow measurement can show the volume and rate of air that can be forcefully breathed out of the lungs. The measurement should be started after a full lung inhalation. 

During the test, you blow forcefully into the mouthpiece of a device. A peak flow meter (PFM) is used most often. This is a small hand-held device often made of plastic. A PFM is small and light enough to be used almost anywhere. It’s important to use the same PFM on a regular basis. The readings can vary between brands and types of meters. In some cases, the test is done in a healthcare provider's office or a hospital with a spirometer. This device has a hand-held mouthpiece. It's linked by cord to a larger electronic machine.

An important part of peak flow measurement is noting peak flow zones. Peak flow zones are areas of measurement on a peak flow meter. The goal of the peak flow zones is to show early symptoms of uncontrolled asthma. Peak flow zones are different for each person. Your healthcare provider will help find your peak flow zones. The 3 peak flow zones are noted by color and include:

• Green. This means go. The green zone is 80% to 100% of your highest peak flow reading, or personal best. This is the zone you should be in every day. This zone means that air is moving well through the large airways in your lungs. It means that you can do your normal activities and go to sleep without trouble.

• Yellow. This means caution or slow down. The yellow zone is 50% to 80% of your personal best. Measurements in this zone are a sign that your large airways are starting to narrow. You may start to have mild symptoms. These may include coughing, feeling tired, and feeling short of breath. Or feeling that your chest is tightening. These symptoms may keep you from your normal activities. They may also stop you from sleeping well. Contact your healthcare provider if you are in this zone. They may advise treatments or medicine changes to prevent your breathing from getting worse.

• Red. This means stop. The red zone is less than 50% of your personal best. Readings in this zone mean you have severe narrowing of your large airways. Call your healthcare provider because this is a medical emergency. You should get help right away or call 911 if you are having troubling breathing or feeling lightheaded or dizzy. You may be coughing, very short of breath, and wheezing while breathing in and out. Or you may be having retractions. This means the muscles between your ribs are working hard to help you breathe. You may also have trouble walking and talking. Always refer to your Asthma Action Plan.

Why might I need peak flow measurement?

Peak flow measurement using a peak flow meter is useful for people with asthma. During an asthma flare-up, the airways in the lungs slowly start to narrow. This slows the speed of air moving through the lungs. A peak flow meter can help show the narrowing of the airways well before an asthma attack happens. A peak flow meter can help you figure out:

• When to get emergency medical care

• How well an asthma treatment plan is working

• When to use an inhaler

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

• What triggers an asthma attack, such as exercise

A peak flow meter can help you manage asthma. It can give you and your healthcare provider information about how open the airways are in your lungs. The PFM can find small changes in the large airways before you start to wheeze. Using a PFM every day will let you know when your peak flows are starting to drop. This lets you make early changes in your medicine or routine. This can help you keep asthma symptoms from getting worse. The PFM can also find the reading at which you need to call your healthcare provider or go to the emergency room.

Your provider may not advise you use a PFM unless your asthma is moderate or severe and you are managing it with medicine. PFM can also be used to assess other lung problems, such as COPD (chronic obstructive pulmonary disease). COPD includes:

• Emphysema. This is a chronic lung condition that affects the smallest air sacs in the lungs (alveoli).

• Chronic bronchitis. This is long-term inflammation of the bronchi. It creates too much mucus and a chronic cough.

What are the risks of peak flow measurement?

The risks of this test may include:

• Having to take deep breaths may make you feel dizzy or short of breath

• It may trigger coughing or wheezing

Some factors may interfere with the accuracy of peak flow measurement, such as:

• Not breathing in deeply enough to start the test

• Not breathing out strongly enough to show your true level of dysfunction

• Coughing during the test

• Poor seal around the mouthpiece while doing the test

• A dirty meter

• Blocking the mouthpiece with your tongue

• Using medicines that open the airways (bronchodilators)

• Using a different type or brand of peak flow meter. Measurements may vary among brands and types of meters.

How do I get ready for peak flow measurement?

Your healthcare provider will explain the test to you. Ask them any questions you have. You may be asked to sign a consent form that gives permission to do the test. Read the form carefully. Ask questions if anything is not clear.

Tell your healthcare provider if you take any medicines. This includes prescriptions, over-the-counter medicines, vitamins, and herbal supplements.

Make sure to:

• Follow all directions for not eating or drinking before the test

• Follow any other instructions your healthcare provider gives you

Before starting daily peak flow meter measuring, your healthcare provider may have you follow a detailed schedule for 2 to 3 weeks. This is done to find your personal best peak flow measurement. This value will be used as a baseline for your daily measurements. The test should be done at the same time every day. Lung function may change a little at different times over a regular day.

What happens during peak flow measurement?

Peak flow measurement is done 1 or more times daily at the same time of day. Or it is done whenever you are having early signs of an asthma attack. Or you should use it when advised by your healthcare provider. Use the peak flow meter (PFM) before taking asthma medicine. Your provider may advise other times when using a PFM is useful.

In most cases, peak flow measurement follows this process:

1. Before each use, make sure the sliding pointer on the peak flow meter is reset to the 0 mark.

2. Hold the PFM by the handle.

3. Stand up straight.

4. Remove chewing gum, candy, or food from your mouth.

5. Take a deep breath and put the mouthpiece in your mouth. Seal your lips and teeth tightly around the mouthpiece.

6. Blow out as hard and as fast as you can.

7. Note the number where the sliding pointer has stopped on the scale.

8. Reset the pointer to 0.

9. Repeat this 3 times. The 3 readings should be close together. If not, adjust your method.

10. If you cough during a measurement, repeat the measurement.

11. Record only the highest of the 3 readings. Do not average the numbers together. The highest number is called your peak flow or personal best.

12. Use the peak flow meter once a day, or as advised by your healthcare provider. Measure peak flows about the same time each day. A good time might be when you first wake up, or at bedtime.

13. Clean and care for your meter as instructed.

14. If you use a new peak flow meter, you will need to find your new personal best value on the new meter.

15. Your healthcare provider may give you other directions as needed.

What happens after peak flow measurement?

Note which peak flow zone your measurement falls into. Follow the instructions below:

• Green. This means go. Continue to follow your asthma plan as directed by your healthcare provider.

• Yellow. This means caution or slow down. You should tell your healthcare provider at this time. They may tell you to increase or change your medicines. They may give you other instructions to help keep your symptoms from getting worse.

• Red. This means stop. This is a medical emergency. You should get help right away. Take your rescue medicine and call your healthcare provider or go to an emergency room. You may need to call 911.

Your healthcare provider may give you more instructions about what to do for each peak flow zone.

Next steps

Before you agree to the test or the procedure make sure you know:

• The name of the test or procedure

• The reason you are having the test or procedure

• What results to expect and what they mean

• The risks and benefits of the test or procedure

• What the possible side effects or complications are

• When and where you are to have the test or procedure

• Who will do the test or procedure and what that person’s qualifications are

• What would happen if you did not have the test or procedure

• Any alternative tests or procedures to think about

• When and how you will get the results

• Who to call after the test or procedure if you have questions or problems

• How much you will have to pay for the test or procedure