Peak Flow Meter: Uses, Procedure, Results

An important tool for effective asthma monitoring and more

A peak flow meter is a portable device that measures your peak expiratory flow rate (PEFR)—that is, how quickly your lungs expel air during a forceful exhalation after you fully inhale. Regularly conducting a peak flow test at home and tracking the results can help you monitor your breathing status and respiratory disease.

In particular, knowing your normal peak flow rate—and detecting when you are not achieving it—can be an important part of your asthma treatment and asthma action plan.

how to take a peak flow measurement
Illustration by Cindy Chung, Verywell 

Purpose of Test

Peak flow can also help you monitor emphysema or chronic bronchitis, but one of its most common uses is in the management of asthma.

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 the openness of your airways. 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 can:

  • Help you keep track of how well you're breathing on a regular basis
  • Indicate an impending asthma attack or worsening of your asthma symptoms
  • Help you know when it is time to activate your asthma action plan
  • Help you identify asthma symptom triggers
  • Determine whether your management plan is effective or if your symptoms are getting worse and your treatment needs to be adjusted

Peak flow meters can also be used to track any breathing changes in those with emphysema or chronic bronchitis and to determine if treatment plans, including medications, are working.

Peak flow meters are usually recommended for adults and children who are at least 5 years old and have moderate to severe asthma, or in cases where symptoms aren't under control and medication is being adjusted. Although anyone can use the device, it might not be particularly helpful if you have mild asthma and aren't on daily medication.

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.

Because asthma may change gradually, your peak flow measurement may start to decrease hours—and sometimes even days—before you notice any symptoms.

If your child has been diagnosed with asthma and is under the age of 5, using a peak flow meter may be difficult. However, some younger children are able to do it. Even if not, it doesn't hurt to have them practice getting used to how it works so they are prepared when they are older.

Risks

The risks of peak flow measurement are minimal but can include coughing or feeling lightheaded from filling your lungs with air before you blow into the device.

If you begin to feel strange, simply take a deep breath and allow your body and mind to calm down. Mention the experience to your doctor, as it may indicate poor control of your asthma. However, if for some reason you continue to feel "off," uncomfortable, or anxious after a peak flow test, seek urgent medical attention.

While not a direct health risk of the test itself, parents should know that peak flow readings for children are sometimes less reliable than for adults. Measurements can be falsely increased with tongue movements or spitting and decreased with not enough effort in the breath, so it's important to also pay close attention to your child's symptoms—not just their peak flow results.

Before the Test

There is little to do to prepare for peak flow testing, but you will likely need to secure your peak flow meter on your own and be ready to record the information it provides.

Your doctor will probably have you find your personal best peak flow number to figure out what's normal for you before you start taking routine readings, so you should also make sure you are clear about what that involves before beginning.

Choosing a Peak Flow Meter

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.

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.) You may want to ask your doctor for recommendations.

Peak flow meters are relatively inexpensive, especially if you purchase a plastic device with a spring system. These are typically $10 to $25.

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 you find worth considering.

Interestingly, preliminary research suggests that using a digital monitoring device along with a linked smartphone app that records the measurements may help improve the consistency of PEFR monitoring and the reliability of data compared to a standard device and manual log. 

Contact your insurance 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.

Know How to Determine Your Personal Best

Your personal best peak flow is the highest peak flow measurement you obtain over a period of two to three weeks when your condition is effectively controlled, meaning that you feel well and aren't experiencing respiratory symptoms. Testing is typically done two to four times a day at the same times every day.

Although there are "normal" peak flow rates based on a person's height, age, sex, and race, these are 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 establish your personal best peak flow. This measurement is the one against which all your other peak flow measurements will be compared moving forward.

You will receive instructions from your doctor or asthma educator regarding how to go about determining your personal best and what your next steps should be. Ask any questions you have before taking your first measurement.

In particular, be sure you are clear about:

  • Frequency and duration of personal best testing: How many times a day? At what times? For how many weeks?
  • Follow-up: Do you need to make an appointment to discuss peak flow zones and your action plan once you've determined your personal best, or can that be done over the phone?
  • Future testing: How often and at what time of day should you measure your peak flow once your personal best and peak flow zones are established? Should you measure you peak flow before or after you have taken your asthma medication?
  • Testing adjustments: What circumstances might warrant extra measurements? (e.g., sickness, worsening symptoms, an asthma attack, or changing medications)

Record Keeping

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 automatically being tracked digitally. Consider purchasing a pocket-size notebook that you can dedicate to this or download and use a smartphone app designed for this purpose.

You may also want to seriously consider keeping a daily record of your asthma, chronic bronchitis, or emphysema symptoms. Log the medications and doses you're taking, and any 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 treatment plan is working and help you see patterns.

During the Test

How you use the peak flow meter is the same regardless of whether you are finding your personal best reading or doing routine measurements, though the recommended testing schedule may differ.

A peak flow test normally only takes a minute or two. Readings are most accurate if they are taken at the same time every time. 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 all of your doctor's instructions regarding when to perform your peak flow tests.

Pre-Test

Check the peak flow meter for any obstructions or foreign objects, and make sure it is clean and dry before use. Not only can a dirty peak flow meter affect the accuracy of your readings, but it can also potentially make you sick.

Follow the care instructions that come with the device. For the plastic, spring system type, general instructions are to let it soak in a bowl of warm water and mild dish soap for three to five minutes, swish it around, rinse it out, and let it dry completely before use.

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.

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

Throughout the Test

Follow these steps to conduct a peak flow test:

  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, making sure that your tongue is underneath the mouthpiece and that your lips are closed tightly to create a seal around it.
  6. Blow air out as hard and as fast as you can in one breath for no more than one second.
  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. If not, write down the number on the meter at which the marker now rests (spring system) or that shows on your the screen (digital), if not logged electronically.
  8. Repeat steps 1 to 7 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.

After the Test

When you're finished taking these readings, 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.

You can then 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.

Interpreting Results

If you're just starting out and establishing your personal best peak flow, your doctor will review your readings and determine what readings align with which peak flow zones for you. These ranges are color-coded like a stoplight to indicate levels of concern:

  • Green zone: Your asthma is well-controlled.
  • Yellow zone: Your asthma is starting to get worse and needs attention.
  • Red zone: Your condition has become a potential emergency.

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.

If you are at the point at which you are routinely monitoring your peak flow, you will be able to reference your results and your asthma action plan to determine whether your rate is satisfactory (green) or has dropped into the warning (yellow) or danger (red) zones.

Peak Flow Zones  % of Personal Best Meaning
Green 80% to 100% •Condition is stable and well-controlled
•Likely no symptoms
•Keep taking medications as prescribed
Yellow 50% to 80% •Airway is beginning to narrow, though you may not have symptoms yet
•Use rescue inhaler or have medication adjusted if symptoms are occurring (per your action plan)
Red Under 50% •Possible medical emergency
•Airway has significantly narrowed; may be fatal without treatment
•Follow your action plan (rescue inhaler, medication)
•Call for help; never drive yourself to the ER

Follow-Up

Lung conditions, including asthma, have the potential to change, so they 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 with careful monitoring.

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 a particular zone.

A personal best peak flow should be remeasured every year or whenever your doctor recommends, since your condition can change. For kids, this takes into consideration growth and expanding lung capacity.

If you start using a new peak flow meter, you will also need to remeasure your personal best since readings can vary from brand to brand and even meter to meter.

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 the effects of all of your medications, 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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