Using a Peak Flow Meter to Track Symptoms

Why tracking your peak flow is worth the effort

A peak flow meter measures how fast you can blow air out of your lungs – your peak expiratory flow. For people with asthma, it gives an objective number that shows how well your airways are working. Unlike how you feel, a peak flow reading can catch a worsening of your asthma before you notice symptoms. That early warning gives you time to adjust your treatment as set out in your asthma action plan, or to contact your GP or asthma nurse. Used consistently, it helps you and your healthcare team spot patterns and keep your asthma under control.

How to use your peak flow meter correctly

Technique matters. Follow these steps every time:

• Stand up straight. Don't sit down.
• Slide the marker to zero.
• Take a deep breath in.
• Seal your lips tightly around the mouthpiece. Don't put your tongue inside.
• Blow out as hard and fast as you can – like blowing out birthday candles.
• Write down the number. Repeat twice more. Record the highest of the three readings, never an average.

Do this at the same times each day – usually morning and evening. If you use a reliever inhaler, your GP or asthma nurse may ask you to take readings before using it. Keep your meter clean and check its expiry date.

Finding your personal best and understanding your zones

Your personal best is the highest peak flow reading you can achieve when your asthma is well controlled. It's not a predicted value – your own best is what matters. To find it, measure twice a day for two to three weeks when you feel well. The highest reading is your personal best. Your GP or asthma nurse can help confirm it.

Your asthma action plan will use a traffic light system:

• Green zone: 80–100% of personal best. Asthma is under control. Keep taking your preventer inhaler.
• Yellow zone: 50–79%. Asthma is getting worse. Follow your action plan, use your reliever inhaler more often, and contact your GP or asthma nurse if you stay in this zone for more than a day or two.
• Red zone: Below 50%. Medical emergency. Use your reliever inhaler immediately and call 999 if you are struggling to breathe, cannot speak in full sentences, or your lips or fingers turn blue.

Recording your readings in a useful way

Record your readings in a diary or on your phone. Note the date, time, and number. Add a few words about how you felt – for example, "wheezy after walking upstairs" or "woke up coughing at 3am". Also note possible triggers like pollen, cold air, or exercise. This context turns numbers into a meaningful story for your healthcare team.

• Record the best of three blows, not an average.
• Morning readings are often lower than evening ones.
• Note any reliever inhaler use.
• Keep your diary with you at GP or asthma nurse appointments.
• Don't panic over one low reading – look at the trend over several days.

Sharing changes with your healthcare team

Bring your peak flow diary to every asthma review. Don't wait for a scheduled appointment if you notice a sustained drop – for example, if you are in the yellow zone for more than 48 hours, or your readings are getting lower day by day. Phone your GP surgery and explain. They should arrange a same-day telephone or face-to-face appointment. If you have an asthma action plan, follow it. If not, ask for one.

Be specific. Instead of "my peak flow has been a bit low", say "my personal best is 450, and for three days my morning readings have been 320 to 350". That detail helps your clinician decide whether to change your medication, add steroid tablets, or investigate other causes.

When to seek urgent help

A peak flow meter is a tracking tool, not a substitute for emergency care. Call 999 or go to A&E if you have a severe asthma attack. Signs include: your reliever inhaler is not helping or you need it more than every four hours; you are too breathless to speak in full sentences, eat, or sleep; your breathing is getting faster and you feel exhausted; or your lips or fingers turn blue or grey. If your peak flow is below 50% of your personal best and does not improve after using your reliever inhaler as directed, treat it as an emergency.

For everyday management, keep your meter visible, use it as part of your routine, and remember the numbers are there to help you, not worry you. With practice, tracking your peak flow becomes second nature – and gives you a clearer, calmer picture of your asthma.