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What is peak expiratory flow?

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

Medical Reviewers: William C. Lloyd III, MD, FACS Last Review Date: Sep 4, 2016

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