Peak Flow Measurement
What is peak flow measurement?
Peak flow measurement is a quick test to measure air flowing 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.
Peak flow measurement can show the amount 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 handheld device 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 handheld mouth piece that’s attached 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 set differently
for each person. Your healthcare provider will help determine 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. When your measurements
are in this zone, air is moving well through the large airways in your lungs. It means
that you can do your usual 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, such as coughing, feeling tired, feeling
short of breath, or feeling like your chest is tightening. These symptoms may keep
you from your usual activities or from sleeping well.
- 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. This is a medical
emergency. You should get help right away. You may be coughing, very short of breath,
wheezing while breathing in and out, or having retractions (the muscles between the
ribs are working hard to help you breathe). You may also have trouble walking and
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 large airways in the lungs slowly begin 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
- When to get emergency medical care
- How well an asthma treatment plan is working
- When to stop or add medicine as directed 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 detect
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 allows you to make
early changes in your medicine or routine to help keep asthma symptoms from getting
worse. The PFM can also identify the reading at which you need to call your healthcare
provider or go to the emergency room.
Your healthcare 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:
- Emphysema. This is a chronic lung condition that affects the smallest air sacks in the lungs
- Chronic bronchitis. This is long-term inflammation of the bronchi. It creates excess mucous and a chronic
What are the risks of peak flow measurement?
All procedures have some risks. The risks of this procedure may include:
- Having to take in deep breaths may make you feel dizzy or short of breath
- It may trigger coughing or wheezing
Certain factors may interfere with the accuracy of peak flow measurement, such as:
- Not breathing in deeply enough to start the test
- Not breathing out forcefully enough to show your true level of dysfunction
- Coughing during the test
- Poor seal around the mouthpiece while performing the procedure
- A dirty meter
- Blocking the mouthpiece with your tongue
- Use of medicines that open the airways (bronchodilators)
- Use of a different type or brand of peak flow meter, as measurements may vary among
brands and types of meters
How do I get ready for peak flow measurement?
Your healthcare provider will explain the procedure to you. Ask him or her any questions
you have. You may be asked to sign a consent form that gives permission to do the
procedure. 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:
- Not eat a heavy meal before the procedure, if instructed by your healthcare provider
- 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 over 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
What happens during peak flow measurement?
Peak flow measurement is done 1 or more times daily at the same time of day, or whenever
you are having early signs of an asthma attack. Or you should use it when directed
by your healthcare provider. Use the peak flow meter (PFM) before taking asthma medicine.
Your healthcare provider may advise other times when using a PFM is useful.
In most cases, peak flow measurement follows this process:
- Before each use, make sure the sliding pointer on the peak flow meter is reset to
the 0 mark.
- Hold the PFM by the handle.
- Stand up straight.
- Remove chewing gum, candy, or food from your mouth.
- Take a deep breath and put the mouthpiece in your mouth. Seal your lips and teeth
tightly around the mouthpiece.
- Blow out as hard and as fast as you can. A “fast blast” is better than a “slow blow.”
- Note the number where the sliding pointer has stopped on the scale.
- Reset the pointer to 0.
- Repeat this 3 times. The 3 readings should be close together. If not, adjust your
- If you cough during a measurement, repeat the measurement.
- Record only the highest of the 3 readings on a graph or in a notebook. Do not average
the numbers together. The highest number is called your peak flow or personal best.
- Use the peak flow meter once a day, or as directed 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.
- Clean and care for your meter as instructed.
- If you use a new peak flow meter, you will need to find your new personal best value
on the new meter.
- Your healthcare provider may give you other instructions 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.” You should continue to follow your asthma plan as directed by your
- Yellow. This means “caution” or “slow down.” You should tell your healthcare provider at
this time. He or she may tell you to increase or change your medicines. He or she
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.
Your healthcare provider may give you more instructions about what to do for each
peak flow zone.
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 will you get the results
- Who to call after the test or procedure if you have questions or problems
- How much will you have to pay for the test or procedure