Measuring your peak flow, alongside keeping a note of your asthma symptoms, is a simple but useful way to help you manage your asthma better.
- Keeping a diary of your pattern of scores helps you and your GP know what peak flow scores to expect when you’re well, and what scores suggest your asthma is getting worse.
- You might find it hard to admit that you’re not feeling well, or not notice asthma symptoms. A low peak flow reading can help you spot when your asthma is getting worse.
- And if you’re getting good scores, it can make you feel more positive about your asthma and see what a difference you can make by taking your asthma medicines every day.
Peak flow is a measure of how quickly you can blow air out of your lungs. You measure it by blowing as hard as you can into a small hand-held device called a peak flow meter.
If you manage to blow out quickly and forcefully, you should get a high score. This tells you that your airways are open and working well.
If your airways are tight and inflamed, you won’t be able to blow into the meter as quickly, and your peak flow score will be low.
This could be a sign that your airways are struggling and that your asthma is getting worse.
Using a peak flow diary to record your scores will:
- Help you feel confident that your medicines are working. It’s especially useful if you’ve changed your medicine or dose.
- Get an early warning if your airways are struggling, even if you’re feeling OK, so you can take quick action to avoid an asthma attack. Read our advice on what to do if you’re having an asthma attack
- Get a better idea of what’s going on in your lungs so you can explain your asthma to friends, family and your GP.
- Identify triggers or allergies that could be making your asthma worse. We’ve got lots of advice on what might trigger your asthma
You can get a peak flow meter from your GP, asthma nurse or pharmacy.
When you first get a peak flow meter, ask your GP, asthma nurse or pharmacist to show you how to use it and how to take a reading.
Take these steps to make sure you use your peak flow meter correctly:
- Pull the counter back as far as it will go
- Stand or sit upright – choose what’s most comfortable for you, and always do it that way
- Take a deep breath
- Make sure your mouth makes a tight seal around the mouthpiece
- Blow as hard and fast as you can into the meter
- Write down your score (the number next to the pointer)
- Do this three times in a row so you get three scores. All three scores should be roughly the same. Use the highest of these scores to fill in your peak flow diary
Download a peak flow diary and instructions.
"If you’re finding it difficult taking your peak flow, or if you feel breathless or tight-chested afterwards, speak to your GP or asthma nurse, or call the Asthma UK Helpline for advice on 0300 222 5800 (Mon – Fri; 9am-5pm),” says Asthma UK specialist nurse Kathy.
You can also email the Asthma UK Helpline directly with your peak flow questions by using our Helpline Contact Form or chat to the nurses on WhatsApp (07378 606728)
Video: How to take your peak flow readingAsthma UK nurse, Suzanne, demonstrates how to use your peak flow meter to get a reading.
Transcript for 'How to take your peak flow reading'
0:05 To take your peak flow reading make sure you’re either sitting in a chair or standing up
0:10 but always do one or the other.
0:13 Your peak flow meter has a small arrow and you need to push this right to the top near the mouthpiece.
0:21 Then hold your peak flow meter like so, so your fingers are not going over the arrow.
0:26 Take a deep breath in and then you blow hard and fast into the mouthpiece like this.
0:35 Wherever the arrow goes, next to which number, that would be your peak flow
0:38 score which you can then plot in your peak flow diary.
Measuring peak flow is one way you can manage your asthma well.
For your peak flow scores to be really useful, you need to:
- Check your peak flow twice a day, every day to get a useful pattern of results.
- Check it at the same time every morning and every evening.
- Use your peak flow meter before you take your asthma medicine otherwise it will change the score.
- Use your best effort every time you blow into the meter so you’re comparing like with like.
- Use the same peak flow meter every time.
Whether you’re recording your peak flow every day, or for a set period of time as advised by your GP or asthma nurse, you’ll get the most out of your peak flow diary if you use it alongside a written asthma action plan.
This will tell you what to do if you notice symptoms, or if your peak flow drops below a certain score.
Read our advice on how an asthma action plan can help you manage your asthma.
‘It’s a good idea to check your peak flow throughout the year even when you’re well. This means you can monitor seasonal changes in your airways and identify any triggers like cold weather or pollen,’ says Asthma UK GP Dr Andy Whittamore.
Your peak flow scores are personal to you.
They vary depending on your age, height and whether you’re male or female.
Peak flow scores also vary at different times of the day. It’s normal for your score to be slightly lower in the morning, as peak flow falls overnight, although this can also be a sign that your asthma isn’t well controlled.
Keeping a diary of your own personal peak flow scores over time will help you and your GP know what score to expect when you’re well, and what scores suggest your asthma is getting worse.
How to find your best peak flow score
The score that’s usual for you when you’re well is sometimes called your ‘best score.’
Knowing your personal best peak flow score helps you know what’s a good score for you, so you can feel confident that you’re managing your asthma well.
If you’re using your medicines as planned and following your action plan, you should stay close to your personal best score most of the time.
When you use your peak flow meter, do it three times in a row and record the highest of the three scores in your peak flow diary.
What does a low peak flow score mean?
There may be times when your peak flow score is lower than your usual score.
If you’re not recording scores that are close to your best score, it may be a sign that your asthma is getting worse.
Talk to your GP or asthma nurse about what low scores you need to look out for. When you get this score you need to take action.
Either see your GP or asthma nurse or follow the steps you’ve agreed in your asthma action plan.
- Get into a good routine. Try to take your peak flow every day, twice a day. You might find it helps if you write down exactly when you’re going to take your peak flow so you can stick to it, for example, ‘I’m going to do my peak flow before I leave the house in the morning and before I go to bed at night.’
- Don’t worry if you forget one day – just pick it up again the next day to get a useful pattern of scores
- Keep your peak flow meter with your preventer inhaler to make life easy – and keep your peak flow diary and a pen with them too
- Don’t forget to record symptoms alongside your peak flow and jot down what you’ve been doing, for example, ‘I exercised on Tuesday’ or ‘I came into contact with a pet.’ If your symptoms change but your peak flow score is the same, you still need to book an appointment with your GP or asthma nurse
- Take your peak flow diary to your asthma review and any other asthma appointments to show your GP, asthma nurse or consultant how your asthma has been.
Last updated October 2019
Next review due October 2021