Peak Flow Meter Vs Spirometer

Peak Flow Meter Vs Spirometer

Peak flow meters are different from spirometry. To learn more about Peak Flow Meter Vs Spirometer, read this blog! 

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There are two types of tests used to for diagnosing and monitoring asthma – a peak flow meter and a spirometer. Find out the key differences between the two.

If you suffer with asthma, you will be well versed in the different tests which can be carried out in order to assess your lung function and overall health.

A spirometer and peak flow meter can both be utilized as a way to test just how well your lungs are functioning. But it’s important to note that whilst both are useful tools in the diagnosis and management of asthma, they are used in different ways, both offering different purposes. 

Read this helpful guide to find out the definitions of each and the key difference between them, to help you take control of your condition.

What Does A Spirometer Do?

So, first things first, what exactly can a Spirometer achieve and what is it used for in the world of lung function?

As a simple, quick, and painless way to check your lungs and airways, the NHS state that a spirometer can be used as a way to diagnose a lung condition, if you feel you are experiencing symptoms OR if your GP feels you may be at risk of developing a certain lung condition.

Despite its effectiveness when it comes to diagnose lung conditions such as asthma and COPD,  a 2015 US study showed that just 47.6% of 134,208 asthma patients had spirometry performed within a year of their diagnosis.

A spirometer measures the total volume of air that can be exhaled or inhaled. It can also measure the rate at which a certain volume of air is expelled from the lungs.

How Does A Spirometer Work?

As a test for lung function, the Connected Spirometer will take place at a scheduled appointment, usually at your GP with a practice nurse.

Before starting, you will be shown by the nurse how to blow into the spirometer. 

You may also have to wear a clip on your nose – this is to make sure all the air goes into the mouthpiece and doesn’t escape anywhere.

When you are ready to be tested, you’ll sit comfortably and:

  • Take a deep full breath in, so that your lungs are completely filled with air
  • Close your lips tightly around the mouthpiece
  • Exhale as quickly and forcefully as you can, making sure you empty your lungs fully

The spirometry test will usually need to be repeated at least 3 times

This is to make sure a reliable result is achieved.

The nurse or other health care professional may then ask you to use your inhaler (salbutamol), wait for 15 minutes, and then repeat the test. 

For some other medication, such as ipratropium bromide the wait may be 30-45 minutes between tests. This is called a reversibility test and is used to see if the medication makes an improvement to your breathing.

What does a Peak Flow Meter do?

On the other hand, a peak flow meter, is a hand-held device used to measure the rate of a person’s air flow (the rate at which air is blown out of the lungs). 

Patients can use peak-flow meters as a helpful way to regularly measure their airflow and work out their maximum speed of expiration.

This is known as the peak expiratory flow (PEF).

Peak flow is a useful tool when it comes to diagnosing asthma. 

If you find that you are experiencing symptoms relating to asthma, your doctor will use a peak flow meter to measure your air flow and  to see how just open your airways are.

How Does A Peak Flow Meter Work?

It’s important to be able to use your peak flow meter correctly otherwise the readings will not be accurate.

In the first instance, your doctor or nurse will show you exactly how to take a peak flow reading and follow the steps below:

  • Initially, you will need to put the marker to zero.
  • Inhale deeply
  • Then seal your lips tightly around the mouthpiece and blow as hard and as fast as you can into the device
  • Take a note of what your reading is
  • Do this again for another two blows, one straight after the other and note the readings. Remember to slide the red indicator back to its start position each time.
  • Record the highest reading, with the date and time. 

Your doctor will work with you to help determine your own scale to use on your meter. This will be based on various factors, including your age, height, gender, and overall health.

In order to use your peak flow meter in the most effective way, you need to ensure that you take your readings every day, and always keep a record of symptoms. 

*This will help you to spot if and when your asthma might be getting worse*

When else might a Peak Flow Meter be helpful?

As a way in which to monitor your asthma, a Peak Flow Meter could also be used in the following instances:

  • When your medication has changed (i.e. a new drug or different dose)
  • Are relying on your blue reliever inhaler more than usual
  • If you know that you have been exposed to one of your known triggers (for example, pollen)
  • If you are feeling generally unwell
  • If your asthma symptoms are keeping you up at night

*Key Differences*

Aside from what each instrument is used for, there are other important differences between a spirometer and a peak flow meter.

Test Results

The first time a patient uses a peak flow meter to measure their lung function, a baseline or personal best is made clear.

From then on, the results of each test will be compared with this initial baseline, and placed into one of three peak flow zones.

Meaning ‘go’, the green peak flow zone is defined as a peak flow that is 80 to 100% of their personal best. This shows stability within the lungs and that they are working as they should.

If the peak flow is between 50 and 80% of the baseline, it shows that the lungs are not working as well as they should. This is the condition, or yellow peak flow zone. Measurements in this zone are a sign that your large airways are starting to narrow and symptoms such as coughing and chest tightness will likely start to appear.

And a reading below 50%? This indicates danger, or the red peak flow zones. In instances such as this, it means stop and indicates an emergency and hospital visit.

A spirometer produces two measurements: forced vital capacity – known as FVC, and forced expiratory volume-one second, called FEV1.

FVC is the maximum volume of air that can be exhaled from full inhalation, in which the patient exhales as forcefully as possible. The FEV1 measures how much air a person can exhale in one second, following on from a forced breath.

When it comes to the spirometry, the value of FEV-1 is divided by the FVC, producing a third number on the test results – the FEV1/FVC ratio. This number highlights the percentage of the lung size – FVC – that can be exhaled in one second. The percentage is then compared with normal values. Furthermore, a flow-volume graph is produced from the test to see how well the lungs are performing.


Whilst a peak flow meter is a small, portable, cylindrical device that fits snugly in the palm of your hand, a spirometer is a larger device that is usually square or rectangular in its shape.

There are various models of spirometer: from a Pneumotachometer, which measures the flow rate by detecting pressure differences across fine mesh, to a Fully Electronic Spirometer, which produces airflow rates without the need for fine meshes.

Depending on the model, there will be differences in the features, such as bulkier mouthpieces or touchscreen elements.


There are vast cost differences between a peak flow meter and spirometer. As the peak flow is a more simple piece of equipment, the costs tend to be quite low. Whereas spirometers can be much more expensive, coming in at around £2000 for one of good quality.