Peak flow measurement animated demonstration

How to use a peak flow meter to obtain a peak expiratory flow rate measurement.

Equipment needed

Apply a new disposable mouthpiece and filter if multiple patients use one device.

Check that the patient has a baseline peak expiratory flow rate (PEFR). Obtain this either from their records - a personal best recorded within the last two years - or, if they have not measured their PEFR within the last two years, calculate it from a predicted PEFR chart.[50] In the case of the latter, note the patient’s age, sex, and height.


As with any procedure, clinicians should not perform measurement of the PEFR where there is lack of consent or understanding by the patient. PEFR measurement is safe and non-invasive, but its accuracy depends on expiratory effort from the patient. Therefore, it may be unsuitable or impractical for young children and patients who are confused.


PEFR provides a measure of airflow obstruction and may be indicated in the diagnosis and management of asthma.

PEFR measurement should be performed in:[50]

  • Patients presenting with an acute asthma attack. Measurement of the PEFR helps to gauge the severity of the attack and inform management

  • Patients with suspected occupational asthma. Serial PEFR readings taken four times per day, both at work and away from work, are the initial investigation of choice.

PEFR measurement should be considered in:[50]

  • Developing a personalised action plan for adults with asthma. The plan may also be symptom-based

  • Adults with a possible diagnosis of asthma. PEFR to measure airflow variability may be used to corroborate a history of recurrent episodic symptoms. Multiple measurements are made over at least two weeks; increased variability may be evident from twice-daily readings.