What measurement is essential for diagnosing asthma?

Spirometry results are essential for diagnosing asthma because spirometry is a pulmonary function test that measures how effectively the lungs are functioning. It provides valuable information about the airflow limitation, which is a hallmark of asthma. Specifically, spirometry assesses parameters such as forced expiratory volume in one second (FEV1) and forced vital capacity (FVC). In asthma, patients typically exhibit a reduced FEV1 and a decreased FEV1/FVC ratio, indicating obstructive airway disease. Importantly, spirometry can demonstrate reversibility of obstruction after the administration of bronchodilators, reinforcing the diagnosis of asthma.

Other measurement methods may provide supplementary information but are not definitive for asthma diagnosis. For instance, pulse oximetry measures oxygen saturation and is not specific to asthma; it indicates hypoxemia rather than airflow obstruction. Peak flow meter readings can help monitor asthma control and severity but are not diagnostic on their own. Chest X-rays may be ordered to rule out other conditions and can show related complications but do not provide information on lung function or asthma diagnosis. Thus, spirometry stands out as the key diagnostic tool in asthma evaluation.