Diagnosis of Asthma

Unfortunately, because different people react to different irritants and allergens there is not one single diagnostic test that can be used to diagnose asthma.

The doctor will take into account the symptoms you describe, your medical history and the medical histories of your immediate family and the way in which your lungs and your breathing respond to bronchodilators, or medications that open up the bronchioles of the lungs.

There are a number of tests that are commonly used to positively diagnose asthma, such as:

* Lung function tests are used to determine if there is an improvement in your breathing following the inhalation of a bronchodilator. If you show more than a 15% improvement then asthma is a possible diagnosis.

* Histamine tests are used to determine if your bronchioles are hyper-responsive to inhaled histamines - agents that can cause allergic reactions and asthma. The concentration of inhaled histamine is gradually increased until it is seen to have an effect on the quality of your breathing, and this concentration is used as the basis of a diagnosis. This test is not used as a diagnostic test in all cases as many asthmatics are not triggered by histamines.

* Skin prick tests are used to identify any allergens to which you may be sensitive and which may trigger asthma. Tiny amounts of common allergens are injected into the skin of the forearm and the area is monitored for a reaction. If after 15 minutes there is no visible swelling, then it may be that you don’t have asthma or that you have asthma which is triggered by a more uncommon allergen.  

Other diagnostic tests are also used, including chest x-rays, trial steroid treatment and peak flow measurement. A diagnosis of asthma is normally achieved quickly and easily, so treatment can start immediately.