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What Does a Peak Expiratory Flow Rate Measure?

Medically Reviewed on 7/22/2020

What is the peak expiratory flow rate measurement test?

Peak expiratory flow rate measures lung strength using a handheld device, usually to diagnose or monitor asthma.

A peak expiratory flow rate (PEFR) is also called peak expiratory flow. It is a simple test that measures a person’s maximum speed of expiration/exhalation. It helps assess the status of the airways and lungs. The test is performed using a small, hand-held device that measures the speed of airflow through the bronchi. A patient can perform the test at home or in an outpatient setup.

Understanding the anatomy

During inhalation, air travels through the nose and/or mouth into the trachea (windpipe). The trachea further divides into two tubes (bronchi) that open into the lungs. Within the lungs, the bronchi branch out into smaller tubes called bronchioles. The end of bronchioles open into little air sacs called alveoli that aid in gaseous exchange. The alveoli are surrounded by blood vessels, through which the exchange of gases, oxygen and carbon dioxide take place.

Why is the peak expiratory flow rate measurement test done?

Indications for peak expiratory flow rate (PEFR) measurement are as follows:

  • Monitoring of asthma
  • Monitoring effects of air pollutants of the respiratory system
  • Monitoring of chronic obstructive pulmonary disease (COPD)

Long-term daily PEFR monitoring or home peak flow rate assessment is performed during exacerbations for patients with:

  • moderate or severe persistent asthma.
  • a history of severe exacerbations.
  • poor perception of airflow obstruction and worsening asthma.
  • a preference for peak flow rate monitoring rather than the use of a symptom-based asthma action plan.

In managing chronic asthma, long-term daily PEFR monitoring may assist with the following measures:

  • Detecting early changes in asthma that may require therapy
  • Evaluating responsiveness to changes in therapy
  • Giving a quantitative measurement of improvement
  • Identifying temporal relations between environmental and occupational exposures and bronchospasm


Asthma is a chronic respiratory disease.
See Answer

When is a peak expiratory flow rate measurement test not done?

The use of a peak expiratory flow rate (PEFR) during acute asthma exacerbations is controversial. Patients who have a history of poor compliance need to have a caregiver or healthcare professional to monitor the patient. Children and young adults are also found to have poor compliance and or perform the test wrong. Moreover, there are no major contraindications for PEFR.

Medically Reviewed on 7/22/2020


Medscape Medical Reference

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