How to Read Peak-Expiratory-Flow Test Results

A peak-expiratory-flow-rate (PEFR or PEF) meter measures how fast and hard a person can exhale. Asthma patients and those with other long-term chronic lung diseases such as COPD and emphysema use this at-home test to determine how well their airways work. You will normally have a higher reading on days when you have better lung function and a lower one when your lung function is not so good.

Loosen any tight clothing that might restrict your breathing and stand or sit up straight when you perform the test. Remove any chewing gum or food from your mouth.

Obtain a peak-expiratory-flow-rate meter, which is a small handheld device with a moveable scale indicator and a mouthpiece. Blow into the meter's mouthpiece as quickly and as hard as you can.

Take the test 3 times in a row and record the highest reading.

Read and record your results over a period of days or weeks and compare them with those on a peak-flow-expiratory-rate chart. You can get a chart at sites such as and (see Resources below).

Analyze your results. A normal reading varies according to your height, age and sex. That is why this test is best used every day to track patterns over time. If you find charts confusing to read, ask your health care professional what your ideal reading should be.

Consult with your doctor if you have lowered peak-flow-expiratory rates over a few days, especially when you have other symptoms like shortness of breath, wheezing or coughing. These might indicate a flare-up in your disease and you can get the right treatment before your symptoms get worse.


Use this test at home to observe your breathing patterns and detect whether your treatments are working or if your illness is getting worse. Read the results daily to see if your health is improving when you start a diet or exercise program or a new treatment for asthma. Your PEF will vary by as much as 15 to 20 percent during the day and is normally lowest in the morning. Therefore, try to take it at the same time every day, preferably in the morning before you take any bronchodilators.


Peak-flow testing isn't as accurate as spirometry, which you receive at your doctor's office. Small changes in peak flow might not mean anything once measured with spirometry. However, a downward trend in your peak-flow rates means that you should call your doctor for more testing. You might have to get your medication changed or be evaluated for other symptoms.

Things You'll Need

  • Peak-flow-meter results chart
  • Peak-flow meter
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