What Should My Normal Peak Flow Be?

Doctor and boy examining lung function test
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Knowing your normal peak flow rate is an important part of asthma treatment, handling an asthma attack, and part of your asthma care plan. Measuring peak flow is simple using an inexpensive device known as a peak flow meter. This portable, handheld device measures how quickly the lungs expel air during forceful exhalation after a full inhalation. This measurement, known as peak expiratory flow (PEF), can help you track your asthma symptoms.

How Is Peak Flow Helpful?

Peak flow measurement can help you identify signs of an impending asthma attack or worsening of asthma symptoms. These are caused by tightening of the airway muscles, which cause the airways to narrow. Peak flow measurement can detect these changes before you notice any symptoms—often hours or sometimes days before. Identifying changes in peak flow can prompt you to use your rescue inhaler to stop symptoms or avoid an asthma attack.

In addition, peak flow measurement can help you identify asthma symptom triggers, determine whether your asthma management plan is effective, or if your asthma symptoms are becoming worse.

What Is Normal Peak Flow?

Your doctor can advise you on how to best monitor your peak flow. It is important to keep in mind that peak flow measurement is most accurate if it is measured at the same time every day— usually once each morning and evening.

Predicted normal values for peak flow are based on a person's age, height, gender, and race. You can see a chart for both adults and children and determine approximately what your maximum peak flow should be. Alternatively, you can go to other sites and enter your age, height, gender, and race and have your peak flow calculated.

However, a more important number is your personal best peak flow. Because your personal best peak flow may vary significantly from your predicted peak flow based on height, age, and gender, your personal best peak flow is very important when you talk to a doctor on the phone or need to go to the emergency department. Equally important, it is the measurement against which all your other peak flow measurements will be compared.

Your personal best peak flow is the highest peak flow measurement you obtain over a period of two to three weeks when your asthma is effectively controlled (you feel well and aren't experiencing asthma symptoms).

How to Find Your Personal Best Peak Flow

To find your personal best peak flow number:

  • Measure your peak flow two times a day during a period of two to three weeks when your asthma is effectively controlled.
  • Always use the same peak flow meter to avoid meter-to-meter variations.
  • Measure your peak flow at the same time every day during that period—usually once in the morning and once in the evening.

Your doctor can help you use your personal best peak flow to track your asthma symptoms. Generally, if your peak flow drops below 80 percent of your personal best, it is recommended that you follow your asthma management plan and begin to track peak flow more frequently until it normalizes.