Spirometry

Spirometry is a test doctors use to diagnose and monitor lung conditions using non-invasive techniques.  

At Guy’s and St Thomas’ Specialist Care, we are committed to providing you with the dedicated respiratory care you need. 

What is spirometry? 

Spirometry is a simple lung function test that we can perform to diagnose or monitor lung conditions. It involves a non-invasive breathing exercise that measures how much air you breathe out in one breath.  

Our team will thoroughly explain the process to you beforehand so you know what to expect.   

Who is a spirometry for? 

A spirometry test is for anyone with an already diagnosed lung condition or those experiencing the potential symptoms of one.  

Symptoms that may need investigating with spirometry include:  

• a persistent cough
• breathlessness

We may also recommend spirometry if you’re over 35 and a smoker.

What does spirometry show?

Spirometry is a practical investigative lung test for diagnosing several conditions.  

Here are some of the conditions spirometry can diagnose:  

• asthma – which causes inflammation and narrowing of your airways periodically
• chronic obstructive pulmonary disease (COPD) – a group of lung conditions that causes your airways to narrow
• cystic fibrosis – a genetic condition that causes your lungs and digestive system to fill with mucus
• emphysema – a lung disease caused by damaged air sacs in your lungs
• pulmonary fibrosis – scarring on your lungs

As well as being a diagnostic tool, spirometry tests can help us monitor your diagnosed lung condition by assessing its severity and checking how it’s responding to treatment. 

Sometimes, we perform a spirometry test before you have surgery to quickly assess your lung function. Doctors also arrange for the test as part of a general health check as you age.     

How to prepare for your spirometry

Preparing for your spirometry test is easy as it’s non-invasive and doesn’t require much preparation. We may advise you to stop smoking for 24 hours beforehand and to avoid alcohol, strenuous exercise and eating large meals a few hours before. 

You may also want to wear loose-fitting clothing so it’s easier to take a deep breath.

How is spirometry performed? 

During a spirometry test, we’ll ask you to breathe into a unique tube attached to a machine (spirometer). 

We’ll get you to sit down and place a soft clip over your nose so you can’t breathe through it.  

Next, we’ll explain what you must do during the test, and we may ask you to practise a few breaths. We’ll begin the spirometry test once you’re happy to proceed.  

We’ll ask you to:  

• take a deep breath to fill your lungs completely 
• close your mouth tightly around the mouthpiece  
• breathe out as quickly and as forcefully as you can until your lungs are empty.

We may repeat the procedure up to three times to get accurate results. Some people may need a repeat test after taking an inhaled bronchodilator medicine (a medication used to manage asthma and COPD). Another test can be beneficial when monitoring your diagnosed condition and seeing if these medicines will help manage your symptoms.   

How long does a spirometry take? 

Spirometry tests can take between 15 and 90 minutes to complete, depending on how many times you need to repeat the test.  

Are there any side effects of spirometry? 

Generally, spirometry has no side effects as it’s considered a safe test. However, you may feel short of breath or dizzy momentarily after completing it. 

We don’t recommend a spirometry test if you’ve recently had a heart attack or have unstable angina, as it requires physical effort to force out a breath. 

You can go home soon after the spirometry test ends and continue your routine.  

Spirometry results

We’ll send your results to one of our specialists for review. It’s unlikely that we’ll give you your results immediately afterwards because it’s crucial that your specialist reviews them and provides an accurate diagnosis or follow-up plan. 

A spirometer machine measures the amount of air you breathe out in a single second and the total volume of air in one breath. 

We’ll review your results by comparing them to a typical result from someone the same age, height and sex as you. Then, we can see whether your lungs are working correctly.  

Obstructive and restrictive spirometry results

A spirometry test can also show if the problems in your lungs are obstructive, restrictive or both.  

In obstructive airway disease, narrowed airways decrease your ability to breathe out, indicating conditions like COPD and asthma.  

Restrictive lung disease is where an inability to expand your lungs fully reduces how much air you can breathe out, which can result in conditions such as pulmonary fibrosis. 

Our team will discuss your results once they’re ready and provide a personalised treatment plan or refer you for further diagnostic tests if necessary.