Bronchoprovocation with methacholine is used to confirm the diagnosis of asthma. The procedure involves inhaling methacholine through a nebulizer attached to a dosimeter that delivers a precise volume of methacholine. The endpoint of the test is the provocational concentration that produces a 20% decrease in FEV1 (PC20). To standardize the procedure, the American Thoracic Society (ATS) recommends that the nebulizer output be calibrated to deliver an output of 0.9 ± 0.09 mL/min.