Breathing and lung function tests

Peak flow test

BLF Joan McCarthy peak flow test

What is it?

The peak flow test measures how fast you can breathe out after you’ve taken a full breath in.

What’s it used for?

If the speed you can breathe out is reduced, that may cause breathlessness - especially during exercise when you have to shift air more quickly. It can also be reduced if you’re unable to take a full breath in.

If you have asthma

This test can help to diagnose asthma and choose treatment. Your GP or nurse should do a peak flow test at your annual asthma review. You may also be asked to monitor your own peak flow at home regularly for a period as part of your asthma action plan.

These results are kept in a peak flow diary to see if your peak flow varies. This can be a feature of asthma, especially if it is not under control.

What happens during the test?

You take the biggest breath in that you can and then blow out as fast as you can into a small, hand-held plastic tube called a peak flow meter. The measurement taken is called your peak flow.

Each time you check your peak flow, you should do three blows, with a short rest in between the blows. The best of the three is the one that should be recorded.

Your health care professional will make sure that your technique is correct, as this may affect the readings.

What will the results look like?

Peak flow scores will vary depending on your age, your height and whether you’re a man or a woman.

Your peak flow reading may be different at morning or at night. It’s the pattern that’s important.

Keeping track of your peak flow can help you spot when your symptoms are getting worse and when you need to take your reliever inhaler or get medical help. 

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Last medically reviewed: February 2017. Due for review: February 2020

This information uses the best available medical evidence and was produced with the support of people living with lung conditions. Find out how we produce our information. If you’d like to see our references get in touch.