Diagnosis of asthma is based on medical history, physical examination, and simple lung function tests such as spirometry.

Diagnosing asthma in babies and toddlers is often very difficult. Symptoms may be the same as those of other diseases, such as infection with respiratory syncytial virus (RSV) or inflammation of the lungs (pneumonia), sinuses (sinusitis), and small airways (bronchiolitis). If you have a very young child, spirometry is not practical, so the diagnosis is made based on your report of symptoms.

Repeated wheezing is the key symptom in children with asthma; however, asthma is not the most common cause of wheezing. Still, if your child wheezes frequently, he or she should be checked for asthma, especially if cough and shortness of breath are also present. Many children and teens with frequent wheezing may have asthma but are not diagnosed with the disease.

To make a diagnosis of asthma in your child, your health professional may look for factors associated with asthma:

• Having wheezing attacks more than 3 times per year lasting longer than 1 day and affecting sleep.
• Having parents with a history of asthma or atopic dermatitis or two of the following three symptoms.
  • Wheezing not associated with colds.
  • Hay fever (allergic rhinitis).
  • A high eosinophil count. Eosinophils are a type of white blood cell often present in allergic reactions.

In an older child, lung function tests can diagnose asthma, determine its severity, and check for complications.

• Spirometry is the most common test to diagnose asthma in older children. It measures how quickly a child can move air in and out of the lungs and how much air is moved. The test helps your health professional decide whether airflow is decreased because of inflamed bronchial tubes and whether the tubes can return to their usual size in a short time after using medication. The test is recommended at least every 1 to 2 years after asthma treatment has begun.
• Testing of daytime changes in peak expiratory flow (PEF) is done over 1 to 2 weeks. This test is needed when your child has symptoms off and on but has normal spirometry test results.
• An exercise or inhalation challenge may be used if the spirometry test results have been normal or near normal but asthma is still suspected. These tests measure how quickly your child can breathe in and out after exercise or after using a medication. An inhalation challenge also may be done using a specific irritant or allergen.
• A bronchoscopy involves using a flexible scope called a bronchoscope to examine the airways. Occasionally airway problems such as tumors or foreign bodies will create symptoms that mimic those of asthma. The test might be done if there is unequal wheezing in the lungs or a poor response to asthma therapy. Biopsies of the airways can be done to look for changes characteristic of asthma.