How to Take a Home Lung Function Test

Assess Your Asthma at Home

A home lung function test measures peak expiratory flow, or PEF. People who have asthma or other lung diseases use peak flow meters to objectively monitor their breathing status and how well their condition is being controlled, allowing them to stay ahead of any impending respiratory issues.

Learning how to perform a PEF and incorporate it into an asthma action plan is an important skill for everyone who has this disease. The process is simple to learn and takes only a few steps.

Doctor explaining lung function test to young boy in clinic
Rafe Swan / Getty Images

Preparation for the Test

To prepare for a home lung function test, you simply need to own a peak flow meter and a chart that shows your expected results. These items should be part of your asthma action plan. Your healthcare provider or asthma educator will provide instructions about how often to perform a PEF and elaborate on any questions or concerns you may have about the task. 

How to Perform a PEF

Before doing a home lung function test, to measure your PEF, remove any food, gum, and excess saliva from your mouth, as such obstructions could interfere with the efficiency of the test. Also check the peak flow meter for obstructions or foreign objects, then follow these eight simple steps to effectively perform the test.

  1. Set your peak flow meter to zero, or the bottom of the scale.
  2. Attach the mouthpiece to the peak flow meter.
  3. Stand up to guarantee you get a deep breath. Stay standing and do not move throughout the test so your results are not affected by a change in position.
  4. Take a deep breath in and place the peak flow meter mouthpiece closely and tightly around your lips. Do not put your tongue inside the mouthpiece.
  5. Breathe out as forcefully as you can, using a huff-like motion, for no longer than one second.
  6. Write down the reading on the gauge.
  7. Place the peak flow meter back to zero before blowing again.
  8. Repeat the blowing and recording process two more times. Go again if you cough or experience any other complications. 

After blowing into the peak flow meter a total of three times, record your highest value for the day. If instructed, also record the other readings.

Is It Dangerous?

You may cough or feel a bit lightheaded the first few times you use a peak flow meter, but this is normal. There are no serious health risks associated with performing a home lung function test, and with practice, it will become easier.

If you begin to feel strange, simply take a deep breath and allow your body and mind to calm down. If you have symptoms, you should talk with your healthcare provider, as it may indicate poor control of your asthma.

If for some reason you continue to feel strange, uncomfortable, or anxious after a test, contact your healthcare provider or another medical professional. 

How to Understand Your Results

Home lung function tests using a peak flow meter monitor the day-to-day status of your asthma. This measurement tells how much air you are able to forcefully breathe out when trying your absolute hardest. With this in mind, you can expect to view your peak expiratory flow after completing the test to see if you need to take action based on your asthma action plan. 

You will then compare your PEF levels to what is expected. Using charts provided by a medical professional that compare your performance against normal values based on sex, race, age, and height, you will either continue your current treatment or need to take action to make sure you are not getting worse. 

Most plans are based on the zone system with green, yellow, and red areas, just like a stoplight.

  • In the green or "go" zone, you are doing well and just need to maintain the status quo. You have minimal symptoms or impairment.
  • In the yellow or "caution" zone, you need to pay more attention and take some steps to prevent the worsening of acute asthma symptoms. 
  • The red zone means you were unable to manage your escalating symptoms. Your action plan will tell you what steps to take, but it's important to seek medical attention.

The goal is to step up your treatment and head off problems before you need to head to your healthcare provider’s office or the emergency room. The red, yellow, and green colors of the stoplight are known by everyone and are associated with a safety mentality. Categorizing asthma in this way makes it easy for parents and patients to understand what they need to be doing and the seriousness of what is going on.

By doing the test regularly, you will determine your personal best measurement and what is normal for you. Your best efforts will eventually be used to determine treatment rather than a strict comparison to the norms based on your height and weight.

Whenever your PEF levels fall below the expected levels set out in your asthma action plan, you should follow the instructions and contact a medical professional immediately. Tackling asthma in a timely manner is key to treating the condition successfully. 

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Lung Association. Measuring your peak flow rate.

  2. UpToDate. Patient education: How to use a peak flow meter.

By Pat Bass, MD
Dr. Bass is a board-certified internist, pediatrician, and a Fellow of the American Academy of Pediatrics and the American College of Physicians.