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.