Test Overview

A home lung function test uses a
peak flow meter or a home spirometer to monitor and evaluate any breathing problems you may have
on a day-to-day basis. A peak flow meter allows you to measure your
peak expiratory flow. A home spirometer allows you to measure your forced expiratory volume at 1 second (FEV1).

If you have a lung
disease, such as
asthma, your doctor may test your peak inspiratory
flow (PIF) and peak expiratory flow (PEF) to measure the amount of air you can
inhale and exhale. This is part of a more complete lung function test.

Why It Is Done

Testing your peak expiratory flow
or your forced expiratory volume at 1 second (FEV1) at home may help:

  • Measure how well your lungs are working if you
    have a long-term (chronic) lung disease, such as asthma.
  • Guide the
    treatment and monitor the effectiveness of treatment for asthma.
    Peak expiratory flow monitoring provides information
    to help people with asthma make better treatment decisions.
  • Monitor
    your lung function if you are regularly exposed to substances at work that can
    damage your lungs (occupational asthma).
  • Monitor for early signs of rejection if you have had a
    lung transplant.

How To Prepare

To perform the peak expiratory flow
(PEF) test, you need a peak flow meter. A peak flow meter is an inexpensive
handheld device you breathe into as hard and as fast as you can.

Read and follow the instructions included with the peak flow meter. Ask
your doctor to show you how to use this device before you use it at home. If
you have questions about how to use a peak flow meter or how to read the
results, talk with your doctor.

If you use medicine to help with breathing (such as for asthma), talk to your doctor about the amount of time you should wait to test your lung function after taking your medicine. You may need to wait a few hours after taking the medicine to do a lung function test. Or your doctor may recommend that you test your lung function in the morning before you take your medicine.

Avoid eating a heavy meal for
about 3 hours before performing a PEF test. Be sure to stand
up to help you take as large a breath as you can. Use the same position every time
you test your PEF. Peak flow monitoring relies on your trying as hard as you
can. For accurate results, be sure to give the test your best
effort every time.

How It Is Done

Before you begin to test your peak
expiratory flow (PEF), remove any gum or food you may have in your mouth.
Follow these steps to use your peak flow meter:

  1. Set the pointer on the gauge of the peak flow
    meter to 0 (zero).
  2. Attach the mouthpiece to the peak flow
  3. Stand up to allow yourself to take a deep
    breath. Make sure you use the same
    position each time you test your PEF.
  4. Take a deep breath in. Place the peak flow meter
    mouthpiece in your mouth and close your lips tightly around the outside of the
    mouthpiece. Do not put your tongue inside the mouthpiece.
  5. Breathe
    out as hard and as fast as you can using a huff. You do not need to breathe out
    for more than a second.
  6. Note the value on the
  7. Move the pointer on the gauge back to 0 (zero) before you
    blow again.
  8. Blow into the peak flow meter 2 more times. Record your
    values each time you blow. If you cough or make a mistake during the testing,
    do the test over.
  9. After you have blown into your peak flow meter 3
    times, record the highest value on your daily record sheet.

How It Feels

Breathing in and out very quickly during
these tests may make you feel lightheaded or may make you cough. If you feel
like you are going to pass out, stop the test.


There are no significant risks linked with
measuring peak expiratory flow (PEF). Breathing in and out very quickly during
the test may make you feel lightheaded or may make you cough. If you feel
lightheaded, stop the test.


A home lung function test uses a
peak flow meter or a home spirometer to monitor and evaluate any breathing problems you may have
on a day-to-day basis. A peak flow meter allows you to measure your
peak expiratory flow
. PEF measures how much air you breathe out when you try your hardest. A home spirometer allows you to measure your forced expiratory volume at 1 second (FEV1). Results from these tests can be compared to
monitor the progression of disease or help measure your response to medical
treatment for a long-term (chronic) lung disease, such as

Peak flows are compared to charts
that list normal values based on age, sex, race, and height. They also can be
compared with your personal best measurement. Check with your doctor or read
the information included with your peak flow meter to find your normal range,
which will vary depending on the type of breathing problems you may have. If
you find abnormal results on any of the tests, discuss them with your

  • Normally, peak flows vary slightly throughout the day. They are
    usually lower in the morning and higher in the afternoon.
  • A person with poorly controlled asthma may have peak flows that
    vary more widely throughout the day.

What Affects the Test

The accuracy of peak flow
monitoring depends on your effort during the test. Results will be inaccurate
if you do not follow directions or do not give your best effort during testing.
The following factors also may affect the results of peak flow

  • Using medicine that expands the airways in the
    lungs within 4 hours before the test may improve test results.
  • Using
    sedatives before the test may worsen test
  • People who have pain while breathing may not be able to breathe
    normally. So the results of their tests may be misleading.

What To Think About

  • Your doctor may do a complete series of lung
    function tests to confirm a lung disease, monitor the progression of lung
    disease, or monitor the effectiveness of treatment. To learn more, see
    the topic
    Lung Function Tests.
  • Checking your
    peak expiratory flow (PEF) provides information that
    may help you decrease your asthma symptoms and keep your lungs as healthy as
    possible. The benefits of better lung function may include improved quality of
    life, fewer emergency department visits, greater personal control and
    confidence, and reduced use of oral steroid medicines, antibiotics, and
    bronchodilators. To learn more about controlling your asthma, see the topic
    Asthma in Teens and Adults.
  • When using a
    home peak flow meter, it is best to use the same meter over time. Different
    brands of meters give different results. If you change your peak flow meter,
    you need to redetermine your personal best measurement using the new
  • Wash your meter according to the manufacturer’s directions
    to prevent growth of bacteria and fungi.
  • PEF is lowest in the early
    morning and highest in the afternoon. If you measure your PEF only once a day,
    do so first thing in the morning before using any bronchodilator
  • People with intermittent or mild persistent asthma may
    not need to check their PEF every day. But if symptoms develop,
    checking peak expiratory flow often for a period of time may be helpful in
    bringing asthma under control.


Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • Holcroft CA, et al. (2003). Measurement characteristics of peak expiratory flow. Chest, 124(2): 501-510.
  • National Institutes of Health (2007). National Asthma Education and Prevention Program Expert Panel Report 3: Guidelines for the Diagnosis and Management of Asthma (NIH Publication No. 08-5846). Available online: http://www.nhlbi.nih.gov/guidelines/asthma/index.htm.


ByHealthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD – Internal Medicine
Specialist Medical Reviewer Robert L. Cowie, MB, FCP(SA), MD, MSc, MFOM – Pulmonology

Current as ofMarch 25, 2017