High probability of asthma What does high probability of asthma mean?
If you have been told that you are at high probability of asthma, it means that your doctor/nurse believes that asthma is the most likely cause for your symptoms, and that there are no other clinical features to suggest an alernative diagnosis.
Whilst high probability means asthma is the most likely diagnosis, it doesnt mean asthma has been confirmed beyond doubt. There are different ways to confirm asthma including:
Lung function tests
Lung function tests are used to check how much air you can breathe in and out, and if there is any narrowing of the airway. Asthma is usually indicated by a narrowing of the airway which can return to normal following treatment. The term for this is: airway obstruction that is reversible.
To confirm asthma, a lung function test should be used to look for narrowing of the airway. The most commonly used test is spirometry. If narrowing of the airway is found, then most people should be checked for reversibility, by inhaling a reliever inhaler and then repeating spirometry 15-20 minutes later to see if the airway narrowing has improved. Whilst spirometry is considered the best test for demonstrating reversible airway obstruction, other tests such as peak expiratory flow monitoring and bronchial provocation can be used. There is more detail about the investigations used to diagnose asthma here
Trial of treatment
If asthma is strongly suspected and you have ongoing symptoms, then starting a treatment to see if the asthma symptoms improve is another way that can be used to confirm asthma.
The treatment should be an inhaled corticosteroid - also known as a preventer or maintenance therapy because it prevents asthma symptoms and asthma attack from occuring. You will be asked to use the treatment for at least 2 months, before being re-assessed. It is often helpful to complete an asthma questionnaire (either the asthma control test or asthma control questionnaire) before and after the trial of treatment so that your symptoms before and after can be easily compared. A trial of treament might demonstrate:
- asthma symptoms are much better - this suggests that asthma is the correct diagnosis. (Some doctors recommend that to be sure it was the inhaler that improved the symtoms you should stop the treatment to see if symptoms come back)
- asthma symptoms are a little better - you may decide to try the treatment for longer (after checking you are using the inhaler correctly), or check lung function tests.
- asthma symptoms are no better - if you have been using the inhaler correctly, no improvement in symptoms suggests that asthma is less likely and further testing is required (you should follow the intermediate probability pathway)
Pro's and con's of a trial of treatment
There are pro's and con's of using a trial of treatment to confirm asthma (which has led to an ongoing debate about the usefulness of a trial of treatment amongst experts).
| Pro's | Con's |
| -It is practical, quick and easy to organise particularly when lung function tests are hard to access / long waiting list. | -It depends on good inhaler technique and remembering to take treatment regularly |
| -If asthma is correct, treatment is started quickly. | -Symptoms may improve coincidentally (i.e. it has nothing to do with taking the medicine) |
What if asthma isnt confirmed?
If asthma hasn't been confirmed by a trial of treatment then investigations for asthma should be completed (you should follow the intermediate probability pathway).
If tests have been conducted but asthma was not confirmed, then there are a number of options:
- undergo further investigations (for asthma or other conditions)
- referral to a specialist
- watchful waiting - if symptoms are mild it might be possible to re-assess after a number of weeks/months
- trial a treatment - if tests are inconclusive and other conditions have been ruled out, sometimes trying a treatment can provide useful information.
Summary
- A high probability of asthma means that asthma is the most likely cause for your symptoms, and that there are no other clinical features to suggest an alernative diagnosis
- Even if asthma is high probability, it is important to confirm the diagnosis with lung function testing or a trial of treatment
- Sometimes asthma is difficult to confirm and may require more assessments, time or tests before a diagnosis can be made
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