A pulmonary function test is an objective measure of lung function, determined by an individual breathing into specialized equipment. When your pulmonary function testing reveals an obstructive pattern with significant reversibility of the obstruction with a bronchodilator (Proventil®, albuterol, Maxair™), you are likely dealing with asthma.
When you have symptoms typical of asthma and normal pulmonary function tests, a methacholine challenge test is the best way to objectively confirm the presence of airway hyper-reactivity, the hallmark of asthma. Asthmatic individuals are highly sensitive to tiny amounts of inhaled methacholine whereas non-asthmatic individuals are generally unaffected. Therefore, if you are asthmatic and inhale methacholine, you will experience a significant decrease in pulmonary functions. This also can be accompanied by asthmatic symptoms, which are quickly reversed with a bronchodilator. A methacholine challenge test is the standard most specialists use to confirm the diagnosis of asthma if you have normal pulmonary function tests.