What Is a Peak Flow Meter?

An important tool for effective asthma monitoring

Doctor and boy examining lung function test
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Knowing your normal peak flow rate is an important part of asthma treatment, handling an asthma attack, and part of your asthma care plan. Measuring your peak flow is simple using a peak flow meter, a portable, handheld device that measures how quickly your lungs expel air during a forceful exhalation after you fully inhale. This measurement, known as peak expiratory flow rate (PEFR), shows how well your asthma is controlled.

Purpose of Test

Part of managing asthma well is keeping tabs on your condition yourself. Monitoring your peak flow can be a big component of this because your peak flow rate number reflects how open your airways are. When your PEFR starts to fall to a certain level, this means that your airway is starting to narrow and that your asthma is getting worse.

Peak flow meters for monitoring your PEFR are usually recommended for adults and children who are 5 years old or older and have moderate to severe asthma, or in cases where your symptoms aren't under control and you're having your medication adjusted. That said, anyone with asthma can use one; it just might not be particularly helpful if you have mild asthma and aren't on daily medication.

Peak flow measurement can also help you monitor chronic obstructive pulmonary disease (COPD) or chronic bronchitis.

Peak flow measurement is used for the following reasons:

  • It helps you keep track of how well you're breathing on a regular basis.
  • It can indicate an impending asthma attack or worsening of your asthma symptoms. This is caused by the tightening of your airway muscles, which makes your airway narrow. Because asthma may change gradually, your peak flow measurement may start to decrease hours—and sometimes even days—before you notice any symptoms.
  • It can help you know when it is time to activate your asthma action plan.
  • It can help you identify asthma symptom triggers.
  • It can determine whether your asthma management plan is effective or if your asthma symptoms are getting worse and your treatment needs to be adjusted.

Depending on the severity of your asthma, your doctor may want you to monitor your peak flow several times a day, once a day, every few days, or just at certain times. The most common recommendation is once a day in the morning before you take your asthma medication. He or she will discuss the best schedule for peak flow monitoring with you.

If your child has been diagnosed with asthma and she's under the age of 5 years old, using a peak flow meter may be difficult. However, some children this age are able to do it. Even if not, it doesn't hurt to have her practice so she can get used to how it works.

Risks

The risks of peak flow measurement are minimal but can include coughing, wheezing, or feeling dizzy or short of breath from filling your lungs with air before you blow into the peak flow meter.

Before the Test

If your doctor wants you to start monitoring your peak flow as part of your asthma care plan, he or she will probably have you find your personal best peak flow number first to figure out what's normal for you. For this, you will use the meter in the same way you will over the course of your monitoring period (see below), though the recommended testing schedule may differ.

You can buy your peak flow meter over-the-counter at a pharmacy, medical supply store, or online. Always use the same brand and model peak flow meter every time to avoid meter-to-meter variations. (If you plan to test at work and at home, for example, you may consider buying two of the same exact devices.)

Personal Best Peak Flow

Your personal best peak flow is the highest peak flow measurement you obtain over a period of two to three weeks when your asthma is effectively controlled, meaning that you feel well and aren't experiencing asthma symptoms.

Although there are "normal" peak flow rates based on a person's height, age, sex, and race, these are normal for large groups of people, many of whom don't have lung diseases. Your normal may be very different than the normal on a generic reference chart, which is why it's so important to know your personal best peak flow reading. Equally important, your personal best is the measurement against which all your other peak flow measurements will be compared.

This number will help your doctor determine your personalized peak flow zones, which are ranges that show whether your asthma is well-controlled (green zone), starting to get worse and needs attention (yellow zone), or has become a potential emergency (red zone). Your doctor will work with you to set up an action plan that tells you exactly what to do if your numbers dip into the yellow or red zones.

Talk with your doctor about any questions you have regarding your peak flow measurement, such as:

  • How many times a day, at what times of the day, and for how many weeks should I measure my peak flow to find my personal best?
  • After I have found my personal best peak flow number, will I need to come in for a follow-up to discuss my peak flow zones and asthma action plan, or can we talk about it over the phone?
  • How often and at what time of day should I measure my peak flow once my best peak flow number and peak flow zones are established?
  • Should I measure my peak flow before or after I've taken my asthma medication?
  • What circumstances might warrant extra measurements, i.e., sickness, worsening symptoms, an asthma attack, or changing medications?
  • Do you have a recommendation for the type of peak flow meter I should use?

A personal best peak flow should be remeasured every year or when your doctor recommends, since asthma can change. For kids, remeasuring takes into consideration their growth and expanding lung capacity. If you start using a new peak flow meter, you will also need to remeasure your personal best since measurements can vary from meter to meter and brand to brand.

Timing

A peak flow measurement normally only takes a minute or two.

Location

You'll do your peak flow measurements at home, school, or work, depending on when and how often your doctor wants you to do them. The meter is a handheld device that does not need to be plugged in, which allows you to test yourself virtually anywhere.

Food and Drink

There are no food or drink restrictions for checking your peak flow. Just make sure you don't have anything in your mouth like gum or candy when you blow into the meter.

Cost and Health Insurance

Peak flow meters are relatively inexpensive, especially if you purchase a plastic device with a spring system. These are typically $10 to $20. There are also digital peak flow meters, which may or may not be covered by health insurance. These can run anywhere from $30 to $100. Certain digital models can record and track your measurements electronically, which may be a feature to consider. Contact your insurance agent or company to discuss what type of peak flow meter they'll cover, as well as what you may need to pay in terms of a co-payment or co-insurance.

During the Test

With time, peak flow tests can become a matter of routine. But the information you gather from each one is valuable, so it's important to keep a manual log of your measurements if they are not being tracked digitally. You may also want to seriously consider keeping a daily record of your asthma symptoms, the medications and doses you're taking, and factors you've been exposed to that you think might trigger your symptoms such as smoke, certain foods, cold, exercise, or high pollen count.

All of this information together can give you and your doctor a more complete picture of how your asthma treatment plan is working and help you see patterns.

Peak flow measurement is the most accurate if it's measured at the same time every time. Follow your doctor's instructions as to how often and when you should check your peak flow.

Pre-Test

Make sure your peak flow meter is clean and dry before you use it. Not only can a dirty peak flow meter affect the accuracy of your readings, it can also potentially make you sick. Follow the care instructions that come with it, but for the plastic, spring system type, general instructions are to let it soak in a bowl of warm water and mild detergent for three to five minutes, swish it around, rinse it out, and let it dry completely.

In most cases, if you're doing a peak flow measurement in the morning, your doctor will want you to do it before you've taken your asthma medication. Be sure to follow his or her instructions on this for the most accurate results.

Throughout the Test

How you use the peak flow meter is the same regardless of whether you are finding your personal best measurement or doing routine measurements.

That said, when determining your personal best peak flow:

  • Measure your peak flow two to four times a day during a period of two to three weeks when your asthma is effectively controlled.
  • Measure your peak flow at the same times every day during that period. Your doctor will tell you what times are best.

Follow your doctor's specific instructions regarding this initial testing period and for subsequent peak flow readings.

To perform an accurate peak flow measurement, follow these steps:

  1. If you're using a meter with a spring system (not digital), make sure the marker on your meter is at 0 or the lowest number. If you're using a digital meter, turn it on.
  2. Attach the mouthpiece if it's not already connected.
  3. Stand up, if possible. If not, sit up straight.
  4. Inhale deeply, filling up your lungs as much as you can.
  5. While holding your breath, put the meter's mouthpiece in your mouth between your teeth, making sure that your tongue is underneath the mouthpiece and that your lips are closed tightly to create a seal around it.
  6. Blow the air out as hard and as fast as you can in one breath.
  7. If you coughed, your tongue got in the way, or you didn't get a good seal, repeat these steps and discard that reading.
  8. Write down the number on the meter at which the marker now rests (spring system) or that shows on your meter (digital), if not logged electronically.
  9. Repeat two more times as soon as you can after you've taken a few normal breaths. The numbers should all be very close together if you're doing it right each time. If they're not, try again until you get three numbers that are similar.

    If you aren't sure that you're using your peak flow meter correctly, take it to your pharmacy or doctor's office and have them check. This can give you reassurance that you're doing it right or help you take steps to adjust your method if necessary.

    Post-Test

    When you're done checking your peak flow, you can go about your normal activities as usual.

    If you're sick with a cold or the flu, make sure to wash your peak flow meter and/or the mouthpiece (depending on whether you're using a digital or plastic one) after each use. Otherwise, clean it according to the manufacturer's instructions, or once a week.

    After the Test

    When you're finished checking your peak flow, record the highest of the three numbers in your peak flow diary or chart. Don't average the numbers together, just use the highest one.

    Interpreting Results

    Once you and your doctor have established your personal best peak flow number and set the numbers that make up your peak flow zones, you should also have developed an asthma action plan. This will tell you what to do in the event that your peak flow begins to drop into the warning (yellow) or danger (red) zones.

    Your regular peak flow measurements will fall into one of these three zones, which your doctor determines based on your personal best peak flow and your symptoms:

    • Green zone: Your peak flow measurements are within 80 percent to 100 percent of your personal best peak flow. Your asthma is stable and well-controlled and you probably aren't having any symptoms. You should keep taking your medications as prescribed.
    • Yellow zone: Your peak flow numbers are 50 percent to 80 percent of your personal best. Like a yellow traffic light, this is a warning and means that your airway is beginning to narrow, though you may not have any symptoms yet. If you do notice that your symptoms are getting worse, these might include coughing, feeling tired, tightness in your chest, or wheezing. You may need to use your rescue inhaler or have your medication adjusted, depending on your specific action plan.
    • Red zone: Your peak flow numbers are under 50 percent of your personal best. This may be a medical emergency. Your airway has significantly narrowed, which can become fatal without treatment. Follow your action plan, which may include using your rescue inhaler, taking a specific medication, and/or calling for emergency help. Never drive yourself to the emergency room when you're in this zone.

      Follow-Up

      Asthma is a disease that has the potential to change, so it should be followed-up on regularly, even when you're doing well. Your medications may need some tweaking here and there, depending on your symptoms. If your asthma has been well-controlled for a long period of time, you may even be able to decrease the dose of your medication.

      Whenever your peak flow numbers start to fall into the yellow or red zones, you may also need to see your doctor to discuss changes to your treatment plan. However, this will depend on what your action plan says, as well as how long you're in the zone.

      You may need to see your doctor for a follow-up visit once you have determined what your personal best is. At this visit, your doctor can set your peak flow zones, go over your action plan, and talk to you about any changes to your treatment plan.

      Other Considerations

      If you ever have any questions about your asthma or the treatment you're getting, be sure to talk to your doctor. You are going to be far more aware of how well (or not) your disease is being controlled than your doctor is, so it's up to you to let him or her know when you have concerns or questions.

      A Word From Verywell

      Since self-monitoring is such an important part of a successful asthma care plan, using a peak flow meter to measure your peak flow can significantly improve the effectiveness of your treatment. As you learn what your asthma triggers are, monitor your peak flow for gradual changes that you may not otherwise notice, and track all your medications (side effects, how well they work), you will also learn more about your asthma, how to manage it well, and what triggers to avoid.

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      Article Sources
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      • Gerald LB, Carr TF. Patient Education: How to Use a Peak Flow Meter (Beyond the Basics). UpToDate. Updated January 3, 2017. https://www.uptodate.com/contents/how-to-use-a-peak-flow-meter-beyond-the-basics
      • Johns Hopkins Medicine. Peak Flow Measurement. The Johns Hopkins University, The Johns Hopkins Hospital, and Johns Hopkins Health System. https://www.hopkinsmedicine.org/healthlibrary/test_procedures/pulmonary/peak_flow_measurement_92,P07755
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      • MedlinePlus. How to Use Your Peak Flow Meter. U.S. National Library of Medicine. Updated August 2, 2018. https://medlineplus.gov/ency/patientinstructions/000043.htm