How Is It Diagnosed?
Since wheezing isn't a sure sign of asthma, babies who have recurrent wheezing are often initially said to have reactive airway disease. Unfortunately, there are no definitive tests that can easily diagnose asthma in babies and toddlers. It's not possible to measure lung function (the volume of air in the lungs and how quickly it's exhaled) in such small children. Physicians and families simply have to monitor the baby over time and see what brings on the wheezing; if it occurs after exposure to dusty areas or spontaneously without an upper respiratory infection, that's a clue that it may be caused by asthma. If a child responds best to asthma treatments, that's another hint.
Since there's a strong link between asthma and allergies, if a child has a history of other types of allergic reactions, such as eczema, I'm more likely to suspect asthma. In addition, a family history of allergies and asthma is a risk factor. Over time, both the parents and the physician will learn what's causing the baby's wheezing and whether those patterns fit with asthma. In my own practice, if a child continues to have bouts of wheezing after the age of 12 months, I'm more inclined to attribute his wheezing to asthma.
At the same time, not every child with asthma will wheeze. Some have milder forms of the disease that give them a chronic cough, which is usually worse at night, or they may develop a chronic cough whenever they get a cold. If there is still uncertainty by age 5, children can then be given a lung function test for a definitive asthma diagnosis.