Peak flow readings are higher when patients are well, and lower when the airways are constricted.
From changes in recorded values, patients and doctors may determine lung functionality, the severity of asthma symptoms, and treatment.

Measurement of PEFR requires training to correctly use a meter and the normal expected value depends on the patient's sex, age, and height.
It is classically reduced in obstructive lung disorders such as asthma.

Due to the wide range of 'normal' values and the high degree of variability, peak flow is not the recommended test to identify asthma.
However, it can be useful in some circumstances.

A small portion of people with asthma may benefit from regular peak flow monitoring.
When monitoring is recommended, it is usually done in addition to reviewing asthma symptoms and frequency of reliever medication use.

When peak flow is being monitored regularly, the results may be recorded on a peak flow chart.

It is important to use the same peak flow meter every time.
Peak flow readings are higher when patients are well, and lower when the airways are constricted. From changes in recorded values, patients and doctors may determine lung functionality, the severity of asthma symptoms, and treatment.
Measurement of PEFR requires training to correctly use a meter and the normal expected value depends on the patient's sex, age, and height. It is classically reduced in obstructive lung disorders such as asthma.
Due to the wide range of 'normal' values and the high degree of variability, peak flow is not the recommended test to identify asthma. However, it can be useful in some circumstances.
A small portion of people with asthma may benefit from regular peak flow monitoring. When monitoring is recommended, it is usually done in addition to reviewing asthma symptoms and frequency of reliever medication use.
When peak flow is being monitored regularly, the results may be recorded on a peak flow chart. 
It is important to use the same peak flow meter every time.
Peak expiratory flow