Peak Expiratory Flow

Medically Reviewed By William C. Lloyd III, MD, FACS
Was this helpful?

What is peak expiratory flow?

Peak expiratory flow is a simple, painless test that measures the speed of exhalation and lung constriction. People with asthma routinely use peak expiratory flow, or PEF, to monitor their asthma control. Your doctor may also recommend peak expiratory flow to monitor such respiratory diseases as pneumonia, cystic fibrosis, severe allergic reactions, and COPD (chronic obstructive pulmonary disease).  

Peak expiratory flow is only one method to monitor your asthma or other respiratory disease. Discuss all of your options with your doctor to understand which options are right for you.

Other procedures that may be performed

Peak expiratory flow is a type of pulmonary or lung function test. Your doctor will likely recommend one or more other pulmonary function tests to diagnose and monitor your respiratory disease. Pulmonary function tests include:

  • Arterial blood gas test to measure oxygen and carbon dioxide levels and other factors in the blood

  • Body plethysmography to determine how much air is present in your lungs when you take a deep breath and how much air is left in your lungs after you exhale as much as you can

  • Bronchoprovocation tests to measure lung function after exposure to factors that commonly trigger asthma. This includes a methacholine challenge test to help diagnose asthma.

  • Lung diffusion capacity to measure how well oxygen moves into your blood from your lungs

  • Pulse oximetry to measure oxygen levels in the blood

  • Spirometry to measure the amount of air and the rate that you inhale and exhale

Why is peak expiratory flow used? 

Your doctor may recommend peak expiratory flow to help you see trends or changes in lung function and understand your overall disease control. Consistent peak expiratory flow testing can help you avoid a serious flare-up of breathing symptoms, such as wheezing and shortness of breath

You will likely perform peak expiratory flow two or more times a day and record your readings. Your healthcare provider will teach you what your readings mean. 

People with asthma routinely measure their peak expiratory flow. Your doctor may also recommend measuring your peak expiratory flow for the following respiratory conditions:

  • Acute bronchitis is lung inflammation generally due to an infection of the bronchial tubes in the lungs.

  • Anaphylaxis is a life-threatening allergic reaction that causes swelling of the breathing passages.

  • COPD (chronic obstructive pulmonary disease) includes emphysema and chronic bronchitis.

  • Cystic fibrosis is a genetic disorder that causes thick, sticky mucus buildup in the lungs and other organs.

  • Pneumonia is inflammation of the lungs, usually due to a viral or bacterial infection.

Your doctor may also recommend measuring your peak expiratory flow if you’ve had a lung transplant.
Measuring peak expiratory flow helps you take charge of your respiratory disease. It is a tool you use to manage your breathing symptoms by: 

  • Determining the severity of your respiratory disease

  • Monitoring how well your treatment is working

  • Detecting flare-ups of breathing problems before they become severe. With practice, you can learn to predict and treat worsening symptoms and even avoid a serious breathing problem before you feel symptoms.

Who performs a peak expiratory flow?

A respiratory therapist or nurse will teach you how to perform peak expiratory flow so you can do it at home. 

The following types of doctors order and monitor peak expiratory flow testing: 

  • Allergist-immunologists and pediatric allergist-immunologists specialize in caring for people with allergies, asthma, and other diseases of the immune system. Pediatric allergist-immunologists further specialize in caring for children from infancy through adolescence.

  • Pulmonologists and pediatric pulmonologists specialize in the medical care of people with breathing problems and diseases and conditions of the lungs. Pediatric pulmonologists further specialize in caring for infants, children and adolescents.

  • Emergency medicine doctors and pediatric emergency medicine doctors specialize in emergency care of people with serious and life-threatening illnesses and injuries. Pediatric emergency medicine doctors further specialize in caring for infants, children and adolescents.

  • Primary care providers including internists, family medicine doctors, and pediatricians offer routine and specialized healthcare and treat a wide range of illnesses.

How do I perform a peak expiratory flow?

You will use a small hand-held device called a peak flow meter. It has a mouthpiece at one end and a scale with an arrow that moves to show your reading. The peak flow meter is light, portable, and does not require electricity or batteries. 

Proper technique is important for accurate peak expiratory flow readings. It may take a bit of practice to master. Taking a reading takes one to two minutes and generally involves these steps: 

  1. Loosen tight or restrictive clothing.

  2. Stand up straight and breathe in as deeply as possible. You can sit up straight if needed.

  3. Blow into the mouthpiece as hard and fast as possible. Make sure your lips make a good seal on the mouthpiece.

  4. Perform this process three times in one session. Be sure to move the arrow indicator back to zero before each reading.

  5. Record your highest flow rate, how you are feeling, and your current situation. For example, record what you were doing when any symptoms started, the severity of your symptoms, and if your medication helped.

  6. Measure your peak expiratory flow every morning before taking your regular medication, when you have symptoms, and after taking medication to treat sudden breathing symptoms. Your doctor may also recommend other times to measure your peak expiratory flow.

Will I feel pain with peak expiratory flow?

Your comfort and relaxation is important and will help you get the most accurate readings. Performing peak expiratory flow is not painful. However, it can sometimes trigger coughing, which may be a symptom of worsening breathing problems. Notify your doctor as recommended for coughing and any other symptoms.

What is a normal peak expiratory flow reading?

Normal peak expiratory flow readings vary widely based on age, height, sex, and other factors. Your doctor, respiratory therapist, or nurse will develop an individualized chart to help you understand your readings. The chart is based on your personal best peak expiratory flow reading. 

Your chart is divided into three colored zones that match a traffic light concept:

  • Green means safe. Readings that are 80% to 100% of your personal best peak flow measurement fall into the green zone. Green readings mean your respiratory disease is under control.

  • Yellow means caution. Readings that are 50% to 79% of your personal best peak flow measurement fall into the yellow zone. Yellow readings mean your respiratory disease is getting worse. You may need to use quick-relief medications or other medications, as directed by your doctor.

  • Red means danger. Readings that are below 50% of your personal best peak flow measurement fall into the red zone. You may need to use quick-relief medications and seek immediate or emergency medical care.

What are the risks and potential complications of peak expiratory flow? 

Measuring your peak expiratory flow is a safe procedure. Do not share your peak flow meter with others or use someone else’s device. This could spread infection.

How do I prepare for my peak expiratory flow?

You are an important member of your own healthcare team. Peak expiratory flow readings are the most helpful if you thoroughly understand your treatment plan and how to perform the test properly. Tell your doctor, nurse, or respiratory therapist if you have questions or are unsure how to perform the test. 

Questions to ask your doctor, respiratory therapist, or nurse

It is common for patients to forget some of their questions during a doctor’s visit. You may also think of other questions after your appointment or after you leave the hospital. Contact your doctor with concerns and questions before your procedure and between appointments.

It is also a good idea to bring a list of questions to your appointments. Questions can include:

  • Why do I need to measure my peak expiratory flow? Are there other options for monitoring my condition?

  • How often and how long will I need to measure my peak expiratory flow?

  • What things should I record in addition to peak expiratory flow readings?

  • What are the safe, cautionary, and dangerous readings for me?

  • Who should I call if my readings are getting worse?

  • How will I know if I should call the doctor or go to the emergency room for more treatment?

  • How should I take my medications?

  • When should I follow up with you?

  • How should I contact you? Ask for numbers to call during and after regular hours.

Was this helpful?
Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Nov 10
View All Lungs, Breathing and Respiration Articles
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.