Asthma and Lung Function Tests (PDF)
Measuring Asthma
Your doctor may ask you to have a lung function test (a breathing test) to help identify if you have asthma or work out how severe your asthma is. There are two breathing tests used for asthma - spirometry and peak flow measurement. Both measure how well your lungs are working and how much your asthma affects your breathing.
Spirometry
Spirometry is the most accurate breathing test for asthma and is often used for diagnosis. An instrument called a spirometer is used.
Doctors use spirometry to:
· help identify if you have asthma;
· help work out how severe your asthma is; and
· identify if your asthma is getting worse.
Spirometry accurately measures and records the amount of air breathed into and out of the lungs. The results show how narrow the airways in your lungs are. Spirometry also helps your doctor to decide what medications to prescribe for you or whether the dose of your current medication needs to be increased or decreased.
What will I have to do for a spirometry test?
Your doctor should explain before the spirometry test what it involves. She/he may conduct the spirometry test at the surgery or send you to a hospital laboratory to have a done, in which case the person doing the test should explain what needs to be done.
You will be asked to:
· stand or sit up as straight as possible and blow into a mouthpiece which is part of the spirometer; and
· make sure you have your mouth correctly over the mouthpiece, and then blow as hard as you can for six seconds, if possible.
Your doctor will repeat the test three times in order to get the best result. You may also be asked to take some puffs from a blue reliever puffer (Ventolin, Airomir, Asmol, Bricanyl). This will show whether medication has an affect on your airways and will help your doctor to assess your dose of asthma medications.
Once the results of the spirometry test come back, your doctor should explain the results to you. Most adults, and children over 7 years of age, can perform spirometry and produce reliable results.
Peak flow
A peak flow meter gives an idea of how narrow your airways are by measuring the maximum, or peak, rate at which you can blow air into it. Peak flow helps you see how much your airways are changing, but is not the recommended test to identify and diagnose asthma.
If you use asthma medications every day your doctor may advise you to use a peak flow meter to help you look after your asthma at home. Generally children over the age of 7 are able to learn the correct use of a peak flow meter.
Peak flow measurement is most often used as part of a written asthma action plan, developed with your doctor to help you to recognise:
· when your asthma is getting worse; or
· when you may need to increase your medication.
A peak flow meter is only one tool available to help control your asthma, if you are feeling unwell see your doctor.
It is important to find your ‘best’ score by recording your peak flow scores every day for one to two weeks when you are well. This score can then be used as a guide for you and your doctor to adjust your asthma management. When your asthma is not as well controlled your peak flow score will be less than your ‘best’.
How to use a peak flow meter
Your doctor, or other health professional such as a nurse, pharmacist or asthma educator, will show you how to use your peak flow meter correctly.
These are the key steps to using the meter:
1. Sit upright or stand;
2. Hold the peak flow meter level, so that the indicator faces upwards. Make sure the indicator is on zero or 'start';
3. Take in as deep a breath as possible;
4. Place your lips tightly around the mouthpiece and blow as hard and fast as you can;
5. Check your score on the meter;
6. Repeat steps 1-5 two more times; and
7. Record the highest score out of the three scores.
If your airways are narrower than usual, the peak flow meter will have a lower score than your ‘best’. When your airways are wide open, the score will be at or close to your ‘best’. What each person should score depends on their height, age and sex and so will vary from person to person.
Always use the same peak flow meter for each measurement as readings may vary slightly between different peak flow meters. It is a good idea to take your own peak flow meter with you when you visit the doctor.
Other times you may need to use a peak flow meter
A peak flow meter may also be used to monitor your asthma when:
1. You leave hospital.
2. You need to take your blue reliever puffer more often.
3. You are getting a cold or you don't feel as well as usual.
4. You have been near a known trigger.
5. Your medication is changed or new medication is started.
6. You are waking at night with your asthma (a sign of poorly controlled asthma).