For many patients with allergies, respiratory issues are an important part of their overall clinical picture. The most common respiratory issues in allergy patients are asthma and allergic rhinitis. Lung function testing can play an important part in both the diagnosis and the monitoring of ongoing respiratory allergy, and in our clinics we have two types of lung function testing available. One is a computerised spirometer and the other is an exhaled nitric oxide meter.
What is a lung function test?
Lung function tests are designed to help in the diagnosis and monitoring of respiratory conditions. A spirometer is a device that measures the flow and volume of air that is exhaled by a patient. These values are used to estimate the calibre of airways and the ease at which air passes through them. This can be extremely helpful at diagnosing conditions such as asthma. Another type of lung function test is an exhaled nitric oxide meter. This is a device that measures the tiny amounts of nitric oxide present in exhaled breath and can be an indicator of inflammation in the airways, which can be an important component of conditions such as asthma. Nitric oxide is a chemical that is produced by the lining of the airway when it is either inflamed or irritable and thus raised levels can be a sign of poor asthma control. Of course, both lung function tests need to be interpreted as part of a wider clinical picture by somebody with experience at doing so.
What can lung function tests detect?
These lung tests can be useful in getting an initial diagnosis by looking at the flow-volume loop from a computerised spirometer as well as the levels of exhaled nitric oxide in the breath and taken in the context of the clinical history. The tests can be further useful at monitoring the progress of conditions such as asthma, and together with ongoing symptoms, allow the doctor to make an estimation of how well, for example, asthma is controlled and whether more medication may be required.
Preparing for your breathing test?
No special preparation is required although generally speaking, children under the age of five will be unable to do lung function testing because of the coordination required to do this. For some people, one or other of their lung function tests may prove challenging because of the coordination required, but this is usually surmountable with guidance and practice from the clinician doing the test with you.
What does a lung function test involve?
Computerised spirometry requires the patient to take a deep breath in, place the mouthpiece in their mouth and create a tight seal around it and then breathing out as hard and as fast as they can. This will be done on a number of occasions to ensure a reliable and reproducible result. Exhaled nitric oxide requires a deep breath in followed by the mouthpiece placed in the mouth with a tight seal, followed by a steady exhalation. The speed of exhalation will be guided by a graphic on the device that tells you whether to breathe faster or slower. Again, the test will be repeated in order to ensure a reproducible result. Each test only takes a few minutes although it may take a little while to get the technique right in the first place. The output of a computerised spirometry test is a printout that includes a range of different values relating to the flow of air through the measuring device and also a graphical representation of the flow-volume loop. All of these provide useful information that can help towards making an assessment of lung function. With exhaled nitric oxide measurement, a number is returned which represents the number of parts per billion of nitric oxide. The higher the number, the more likely it is that there is meaningful airway inflammation. Both tests provide immediate results that can then be discussed with your doctor.
How accurate are lung function tests?
Lung function tests provide extremely useful information for diagnosis and ongoing monitoring but have to be taken in the clinical context of the patient at that time. Your doctor is an expert at using this information together to come up with the most appropriate treatment plan tailored to the individual.
Professor Adam Fox
Date reviewed: November 2021
Adam Fox is a Professor of Paediatric Allergy with over 20 years experience in both the NHS and private sector. Professor Fox is Commercial Medical Director at Guy’s & St Thomas’ Hospitals NHS Foundation Trust and Professor of Paediatric Allergy at King’s College London and the founding Director of the KCL Allergy Academy, a postgraduate educational programme, which was a finalist at the BMJ Awards in 2018.
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