What is the primary method used for diagnosing asthma?

The primary method for diagnosing asthma is through pulmonary function tests, which are crucial for evaluating the function of the lungs. These tests measure how much air a person can inhale and exhale, as well as how quickly they can exhale. The results can indicate whether there is obstructed airflow, which is a hallmark of asthma.

Specifically, tests like spirometry are commonly used, measuring how much air is expelled forcefully after taking a deep breath. They sometimes include assessing the response to bronchodilators, which can demonstrate reversible airway obstruction characteristic of asthma.

While peak flow testing is a useful tool for monitoring asthma and assessing the severity of an asthma attack, it is not primarily used for diagnosing the condition itself. Peak flow meters are simple devices that measure the maximum speed at which a person can exhale air, but they do not give a comprehensive assessment of lung function that would typically be obtained from more extensive pulmonary function tests.

Imaging studies like chest X-rays and CT scans are not standard diagnostic tools for asthma; they might be used to rule out other conditions but do not directly assess lung function or confirm an asthma diagnosis. Thus, pulmonary function tests are the cornerstone of confirming asthma, making them the correct answer.