Peak Flow Test

What is a peak flow test?

Peak flow measurement is a quick test to measure air flowing in and out of the lungs.

The measurement is called the peak expiratory flow rate (PEFR). It’s also known as the peak expiratory flow (PEF). Peak flow measurement is mostly done by people who have asthma.

Peak flow measurement can show:

  • The amount of air breathed in
  • The amount of air breathed out
  • The rate at which the air is breathed in and out from the lungs

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.

Peak flow zones

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 percent 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 percent 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 percent 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 talking.