Your doctor will take a detailed history and examination of your child. Most children with asthma have had symptoms for a long time. If your doctor suspects asthma, a blowing test will be done to check your lung function. It measures how fast you can blow the air out of the lungs. If it is low asthma can be diagnosed.
In children under five, where a blowing test is not possible, the diagnosis of asthma is more difficult. The diagnosis is usually made from a good history and examination, followed by a trial of asthma therapy.