How can spirometry indicate a diagnosis of asthma?

Spirometry is a key diagnostic tool in assessing asthma, and one of its primary functions is to evaluate airflow limitation and responsiveness to bronchodilators. When spirometry results indicate an increase in FEV1 (Forced Expiratory Volume in one second) of more than 200 mL and greater than 12% from baseline after administration of a bronchodilator, it suggests that the patient's airways are hyperresponsive, which is characteristic of asthma.

This significant improvement demonstrates that the airflow obstruction present in asthma can be reversible, which is a hallmark feature of the disease. Asthma is defined by reversible airway obstruction, and the bronchodilator response is a crucial aspect of confirming the diagnosis.

Other options do not accurately represent how spirometry can diagnose asthma. For instance, simply showing a decrease in FEV1 may indicate obstructive lung disease, but it does not specifically confirm asthma without the context of reversibility. Physical symptoms, while important for clinical diagnosis, cannot be quantified through spirometry results. Similarly, a normal peak flow reading does not support a diagnosis of asthma; rather, it may suggest that significant bronchial obstruction is not present at that moment. Thus, indicating an increase in FEV1 post-bronchodilator is essential for