Peak Expiratory Flow Rate (PEFR): Understanding and Monitoring Your Asthma

Peak Expiratory Flow Rate (PEFR or PEF) is a simple measurement that tells you how fast you can blow air out of your lungs. For people with asthma, regularly checking PEF can provide useful information about how well their airways are functioning and whether their asthma may be getting better or worse.

A small device called a peak flow meter allows you to measure your PEF at home in just a few seconds.

Your symptoms tell you how you feel. Your peak flow reading can give you another piece of information about how well your airways are working.

What is Peak Expiratory Flow Rate?

Peak Expiratory Flow Rate (PEFR), commonly called Peak Expiratory Flow (PEF), is the fastest speed at which you can blow air out of your lungs after taking a full deep inhalation.

It is usually measured in litres per minute (L/min).

When the airways become narrower, as can happen during an asthma flare-up, it may become harder to blow air out quickly. Your PEF may therefore fall. For this reason, following your PEF over time can sometimes help identify changes in asthma control. However, one PEF reading should not be interpreted on its own. Your symptoms, treatment, previous readings and clinical assessment are also important.

What is a Peak Flow Meter?

A peak flow meter is a small, portable device used to measure your Peak Expiratory Flow.

It is easy to carry and can be used at home. It’ is usually be a cylindrical device with a mouth piece at one end and a long calibrated scale on the body, with a pointer that can run along the scale. Some meters may have red yellow and green markers as well that can be moved up and down. These are used to mark red, green and yellow zones (see below).

Digital peak flow meters are also available, although they are expensive.

How do I use a peak flow meter?

The exact instructions may vary slightly between devices, but the basic technique is:

1️⃣ Stand up straight if possible.

2️⃣ Set the meter to zero or the lowest position.

3️⃣ Take a deep breath, filling your lungs completely.

4️⃣ Place the mouthpiece between your teeth and close your lips firmly around it.

5️⃣ Blow out as hard and as fast as you can in a single breath.

6️⃣ Note the reading.

7️⃣ Repeat the test as instructed, usually three times.

8️⃣ Record the highest of the three reading on your peak flow chart.

Good technique is important. A weak or slow blow can give you an artificially low reading.

Watch this video by American Lung Association on how to use a peak flow meter:

How to use a peak flow meter

How Can PEF Help in Asthma?

PEF can be useful in several ways.

1. 🔬 It can support the diagnosis of asthma.

Asthma is characterised by variable symptoms and variable narrowing of the airways. Repeated PEF measurements can sometimes demonstrate this variability, particularly when readings are taken over a period of time. However, PEF alone does not prove that you have asthma. Depending on the circumstances, your doctor may recommend spirometry, bronchodilator testing or other investigations.

2. 📈 It can help monitor asthma.

Your PEF can be followed over days or weeks to see whether your airflow is relatively stable or changing. It is particularly useful in patients who have difficulty recognizing symptoms or exacerbations, and also in helping in the diagnosis of occupational asthma.

A sustained fall from your usual readings may be an early warning that your asthma is becoming less well controlled. Appropriate intervention may then be initiated as per your Asthma Action Plan (see below)2

3. 📏 It can help define “zones” in your Asthma Action Plan

Regular monitoring can give you your “personal best” readings. These readings are used to establish an asthma action plan, where specific zones of PEF readings are marked in red yellow and green. A fall in PEF, for example, to a specified number can be used to increase the dose of a prescribed inhaler.

4. 🩺 It can help assess response to treatment

Your doctor may sometimes ask you to monitor PEF when starting or changing asthma treatment. Changes in your readings, together with your symptoms, can help assess whether your asthma is responding.

PEF is most useful when you look at the pattern over time—not just one isolated number.

😎 What Is a Personal Best PEF?

Your personal best PEF is the highest PEF you can achieve when your asthma is well controlled. This is often more useful for managing asthma than comparing your reading with a generic “normal” value.

Your personal best should ideally be established during a period when your asthma is well controlled and according to advice from your healthcare professional.

Once you know your personal best, your asthma action plan can use it as a reference point.

🚦What Is an Asthma Action Plan?

An asthma action plan is a written plan that tells you what to do when your asthma is stable, when it starts getting worse, and when you need urgent medical attention. It is usually prepared together with your doctor. PEF can be included as one of the measurements used in the action plan. A commonly used approach divides readings into three zones:

🟢 Green zone — Doing well

Your PEF is within the range established for you, and your asthma symptoms are under control. You should continue your regular asthma treatment as prescribed.

🟡 Yellow zone — Caution

Your PEF has fallen below your usual range, or your asthma symptoms are becoming worse. This may be a warning that your asthma is losing control. Your action plan should tell you what steps to take.

🔴 Red zone — Medical alert

Your PEF has fallen significantly, or you have significant asthma symptoms.

Your action plan should tell you what treatment to take and when to seek urgent medical help. The exact PEF cut-offs and treatment instructions should be decided with your healthcare professional.

Do not rely on a PEF number alone if you are experiencing severe breathing difficulty.

How Should I Chart My PEF?

If your doctor has advised regular PEF monitoring, recording your readings on a chart makes it much easier to see changes over time, and to achieve all targets listed above.

You may be asked to measure PEF:

• In the morning and evening
• Before and/or after asthma medication
• When you develop symptoms
• Before and after exposure to a suspected trigger
• During a period when your asthma is being assessed

Keep your chart simple

For each measurement, record:

1. Date
2. Time
3. PEF reading
4. Symptoms or use of reliever inhaler

(What is a Reliever Inhaler? See the Main Asthma article for details.)

The purpose is not to become obsessed with every number. The chart helps you recognise a pattern. A gradual fall in your usual readings may be more important than a small difference between two individual measurements.

Download our PEF monitoring handout:

PEF instructions and monitoring chart

What to do when I have a Low PEF Reading?

A low reading does not always mean that your asthma has suddenly become worse. Other possible reasons include:

• Missing prescribed asthma medication
• Incorrect inhaler technique or poor adherence
• Poor peak flow technique, including not taking a deep enough breath before blowing
• Not blowing hard and fast enough
• Problems with the peak flow meter

If your reading unexpectedly falls, repeat the measurement using correct technique and consider how you are feeling.

If low readings persist or you have worsening symptoms, follow your asthma action plan and contact your healthcare professional.

What Are the Limitations of PEF?

PEF is useful, but it is not a perfect measurement. Your result can be affected by your effort and technique. Different peak flow meters may also produce somewhat different readings. PEF should therefore be used consistently and interpreted in context.

A good PEF reading does not mean you should ignore severe asthma symptoms.

If you are struggling to breathe, cannot speak comfortably because of breathlessness, become unusually drowsy or confused, or develop other signs of severe asthma, seek urgent medical attention rather than relying on your peak flow reading.

Where Can I Buy a Peak Flow Meter?

Peak flow meters are available from medical equipment suppliers and pharmacies. If you are purchasing one, make sure you know how to use it correctly and use the same meter consistently when monitoring your asthma.

PEF meters are also available at our associated online store.

Rossmax PF120(A) | Adult Peak Flow Meter

The Bottom Line

A peak flow meter is a simple tool that can help you understand what is happening with your asthma. It can help you:

• Measure how quickly you can blow air out
• Follow changes in your airway function
• Identify a possible deterioration in asthma control
• Monitor your response to treatment
• Contribute useful information to an asthma action plan But remember that PEF is only one part of asthma care. Your symptoms, medications, inhaler technique, triggers and medical assessment all matter. Learn your usual PEF, know your personal best, and understand what to do when your readings fall.

Useful resources on ABK Lung Health Education Portal

🎥 Learn the correct peak flow technique [Peak Flow Meter Technique Video] (Coming Soon)

🧮 Calculate and interpret “variability” in your PEF

HELP PEFR Calculator

📄 Download the PEF Chart handout

PEF Handout - instruction in English and Urdu with 14-day monitoring chart

📝 Download extra pages for longer PEFR monitoring

PEFR mounting chart - extra pages

🌿 Learn more about asthma

HELP Asthma Article

🛒 Buy a peak flow meter

ABK Lung Health Store - Peak Flow Meter - Daraz

Disclaimer

This article is intended for general health education. It does not replace an individual assessment or treatment plan from your healthcare professional.