The Journal of asthma : official journal of the Association for the Care of Asthma
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Methacholine challenge (MCC) is an important diagnostic tool for asthma, especially in patients in whom routine pulmonary function testing (PFT) is normal or equivocal. The basis for a positive test per American Thoracic Society (ATS) guidelines is a methacholine concentration < or = 16 mg/mL that causes a 20% decrease in forced expiratory volume in 1 second (FEV(1)) (termed the PC20 for FEV(1)). There is little information in the medical literature that utilizes other flow rates during MCC, including small airway function parameters such as the forced expiratory flow rate 25-75% (FEF(25-75)). We question whether the FEF(25-75) may be a useful parameter to monitor during MCC and whether it may be predictive of a positive MCC. ⋯ The FEF(25-75) and its decline during a MCC appear to be useful information and potentially predictive of a positive MCC. We suggest that the forced expiratory flow rate 25-75% (FEF(25-75)) be considered as an adjunct to the FEV(1) to define a positive study.