Asthmatics using a peak flow meter to determine the status of their condition should take the following preparatory steps:

• Avoid eating a heavy meal for three hours before taking the test
  
  
• Sit up straight or stand to aid in taking as deep a breath as possible
  
  
• Remove any gum or food from the mouth

Patients who measure their peak expiratory flow once a day should do so first thing in the morning, before using any bronchodilator medication. It is also a good idea to take a second reading in the evening. Usually, peak expiratory flow levels are higher in the evening. Worsening levels at night may indicate that a patient has nocturnal asthma and needs an improved asthma treatment plan.

In addition, patients should take a peak flow meter reading each time symptoms occur and when a rescue medication (such as a short-acting inhaled beta2 agonist) is used – to be sure the medication is working properly. Patients should see an improvement in their peak flow reading after taking the medication. Additional testing may also be required when the patient has a respiratory infection.

Patients using a peak flow meter should use the following steps:

• Move the indicator to the bottom of the numbered scale
• Attach mouthpiece to peak flow meter and stand
• Place mouth on mouthpiece and inhale deeply
• Close lips and teeth tightly around mouthpiece, being careful not to stick the tongue inside the tube
• Blow out hard and fast for no more than one second

The peak flow meter will provide a numerical result during or just after the exhalation. Patients should record the number, then repeat the process twice more. The highest number registered during the three trials should be used to establish a test score. Patients who cough while taking the measurement should disregard the results and take a new measurement. Coughing is likely to cause inaccurate measurements.

A physician should indicate the best times to use the peak flow meter. If a patient cannot use a peak flow meter during this optimal time each day, the patient should try to at least use the meter at the same time each day for consistent results. Use of a peak flow meter will also likely be incorporated into an asthma action plan, which is a written set of guidelines and procedures to follow in the event of an asthma attack.  

Patients will need to record a “personal-best” score when using a peak flow meter. This score will serve as a benchmark against which to measure asthma progress. Although there are predicted “normal” peak flow levels based on height, age and gender, it is better to establish a personal score.

To establish a personal-best score, patients should take peak flow readings at least once a day for two to three weeks. A physician will determine the best time of day to take the readings (usually between noon and 2 p.m.).

The highest peak-flow number recorded during a period when symptoms are under “good control” (when a patient feels good and is not manifesting symptoms) serves as the personal-best score.

Personal-best scores should be remeasured each year to account for growth (in children) and changes in the status of the disease.

Once a personal-best score has been established, ranges are set to help the patient react to subsequent scores. Scores are categorized by three levels:

• Green zone: A score that is between 80 percent and 100 percent of a patient’s personal-best score means no symptoms are present.
  
  
• Yellow zone: A score that is between 50 percent and 80 percent of a personal-best signals that caution is necessary. Follow a physician’s advice for which steps to take.
  
  
• Red zone: A score that is below 50 percent of a personal-best score signals a medical alert. A patient should use an inhaler immediately and a physician should be contacted right away.

Patients should be sure to wash their meter after each use according to the manufacturer’s directions. This will help prevent the growth of bacteria and fungi.

Peak flow meter tests present no significant risks to patients. However, some lightheadedness may result from the repeated blowing that is part of the test. Coughing and wheezing may also occur.