Asthma Diagnosis and Tests

Asthma is defined simply as reversible airway obstruction. Reversibility occurs either spontaneously or with treatment. The basic measurement is peak flow rates and the following diagnostic criteria are used by the British Thoracic Society:

• ≥20% difference on at least three days in a week for at least two weeks;
• ≥20% improvement of peak flow following treatment, for example:
      o 10 minutes of inhaled β-agonist (e.g., salbutamol);
      o six weeks of inhaled corticosteroid (e.g., beclometasone);
      o 14 days of 30 mg prednisolone.
• * ≥20% decrease in peak flow following exposure to a trigger (e.g., exercise).

In many cases, a physician can diagnose asthma on the basis of typical findings in a patients clinical history and examination. Asthma is strongly suspected if a patient suffers from eczema or other allergic conditions—suggesting a general atopic constitution—or has a family history of asthma. While measurement of airway function is possible for adults, most new cases are diagnosed in children who are unable to perform such tests.

In children, the key to asthma diagnosis is the sound of wheezing or a high-pitched sound upon exhalation. Other clues are recurrent wheezing, breathing difficulty, or chest tightness, or a history of coughing that is worse at night. The doctor should also know if the child's symptoms are worse with exercise, colds, or exposure to certain irritants such as smoke, emotional stress, or changes in the weather.

Other information important to diagnosis is the age at which symptoms began and how they progressed, the timing and pattern of wheezing, when and how often a child had to visit a clinic or hospital emergency department because of symptoms, whether the child ever took bronchodilator medication for the symptoms and the nature of the response to medication.