Peak Expiratory Flow Rate

Written by Natalie Phillips | Published on July 20, 2012
Medically Reviewed by George Krucik, MD

What Is a Peak Expiratory Flow Rate Test?

The peak expiratory flow rate (PEFR) is a test that measures how fast a person can exhale (breathe out). This test checks lung functioning, and is often used by patients who have asthma.

Asthma is a chronic condition characterized by ongoing inflammation of the airways. Common asthma symptoms include shortness of breath that worsens with activity, wheezing, and cough. The flow of exhaled air from the lungs may be restricted due to inflammation or congestion from excess mucous.

The PEFR test is commonly performed at home with an inexpensive handheld device called a peak flow monitor. Both non-electric and electric ones are available for purchase. The device is easy to use, and most patients over the age of five can take an accurate reading.

For the PEFR test to be useful, the patient must keep continuous records of his or her flow rate. Otherwise, the patient will not notice patterns that occur when his or her flow rate is low or decreasing.

These patterns can help individuals prevent their symptoms from worsening before a full-blown asthma attack, for example. Individuals will know when they need to adjust their environment or medication, or make an appointment with the doctor.

The PEFR test is also called peak flow.

What Are the Reasons for Taking a Peak Expiratory Flow Rate Test?

The PEFR test is a common, simple test that helps to diagnose and monitor lung problems, such as:

  • asthma
  • chronic obstructive pulmonary disease (COPD)
  • a lung transplant that is not working properly

This test may also be performed at home to determine whether lung disorder treatments are working and to prevent conditions from worsening. Keeping continuous records of peak flow rates may also help the patient to determine whether environmental factors or certain pollutants are affecting his or her breathing.

How Is a Peak Expiratory Flow Rate Test Given?

The PEFR test is done with a peak expiratory flow monitor. This is a simple handheld instrument with a mouthpiece on one end and a scale on the other. A small plastic arrow moves when air is blown into the mouthpiece, measuring the airflow speed.

When you take the test, you will:

  • Breathe in as deeply as you can
  • Blow into the mouthpiece as quickly and as hard as you can. Do not put your tongue in front of the mouthpiece
  • Do this three times
  • Note the highest speed of the three

If you cough or sneeze while breathing out, you will need to start again.

How Often Do I Need to Take the Test?

To determine a “personal best,” patients should measure their peak flow rate:

  • at least twice a day for two to three weeks
  • in the morning, upon awakening, and in the late afternoon or early evening
  • 15 to 20 minutes after using an inhaled, quick-acting beta2-agonist (asthma medicine)

A common beta2-agonist medication is albuterol, which goes by the brand names Proventil and Ventolin. This medication will relax the muscles surrounding the airways and help to increase the caliber of the airway.

How Do I Prepare for a Peak Expiratory Flow Rate Test?

PEFR is a simple test that does not require much preparation. You may want to loosen any tight clothing that might prevent you from breathing deeply. Stand or sit up straight, and focus on the task at hand.

What Are Normal Peak Expiratory Flow Rate Results?

Normal test results vary depending on your age, sex, and height. The results are most useful when compared to your past rates.

You can check your results compared to these ratios provided by MONASH University. This shows normal peak flow rates as related to height (MU):

Height (cm) = PEFR (L/min)

  • 120 cm = 215 L/min
  • 130 cm = 260 L/min
  • 140 cm = 300 L/min
  • 150 cm = 350 L/min
  • 160 cm = 400 L/min
  • 170 cm = 450 L/min
  • 180 cm = 500 L/min

Small changes may not mean anything significant. If you notice a significant fall in your peak flow speed, it may be caused by a flare-up in your lung disease. This is especially possible if other symptoms occur, such as:

  • a worsening cough
  • shortness of breath
  • wheezing or raspy breathing

If you are concerned with the results, you may wish to visit your health care provider and get a more accurate reading with a spirometer. A spirometer is a more advanced peak flow monitoring device. For this test, you will breathe into a mouthpiece that is connected to a spirometer machine that measures your breathing rates.

What Do Abnormal Peak Expiratory Flow Rate Results Mean?

Flow rate lessens when the airways are blocked. Asthma patients may experience low peak flow rates before they develop breathing symptoms.

According to Dr. Daniel R. Neuspiel and Dr. Cheryl D. Courtlandt, if you have asthma and get a peak flow rate that is less than 80 percent of your personal best, you should take your emergency inhaler medication (quick-acting beta2-agonist). If your peak flow rate is less than 50 percent of your personal best, you should take your quick-acting beta2-agonist medicine and seek immediate medical attention (Medscape).

If any of the following symptoms occur, go to the emergency room immediately. They are symptoms of a medical emergency.

  • decreased alertness—this includes severe drowsiness or confusion
  • extreme difficulty breathing
  • bluish color to the face and/or lips
  • severe anxiety or panic caused by the inability to breathe
  • sweating
  • rapid pulse (Pubmed)

What Are the Risks Associated with the Peak Expiratory Flow Rate Test?

PEFR is a safe test. There are no risks associated with this test. In rare instances, you may feel a little light-headed after breathing into the machine several times.

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