Peak Flow Measurement
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)
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.
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
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 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 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,
Emphysema. This is also known as COPD (chronic obstructive pulmonary disease), 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
What are the risks of peak flow measurement?
The risks of this test may include:
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 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:
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 directed 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:
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 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
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.
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