A 7-year-old boy presents with a nocturnal cough and exercise-induced wheeze. Which diagnostic test best confirms asthma?

• A. Chest radiograph
• B. Pulmonary function studies
• C. IgE antibody tests
• D. Complete blood count

Answer: (B)

Diagnosing asthma relies on objective evidence of reversible airway obstruction. In a school-age child with nocturnal cough and exercise-induced wheeze, the strongest confirmation comes from pulmonary function testing using spirometry. This test measures how much and how quickly air is exhaled and can show an obstructive pattern. The key is reversibility: after inhaled bronchodilator, the airways should open and the spirometry values—especially FEV1—should improve significantly (for example, an increase of about 12% and 200 mL or more in FEV1). This demonstrated reversibility distinguishes asthma from other causes of cough and wheeze.

Chest radiographs are not diagnostic for asthma; they’re typically normal or non-specific and are used mainly to rule out other conditions. IgE antibody tests show sensitization but cannot confirm asthma by themselves, and a complete blood count is non-specific for asthma. So the objective demonstration of reversible airflow limitation via spirometry best confirms the diagnosis.