The PD20 but not the PC20 in a methacholine challenge test is device independent

Methacholine challenge tests aid in the diagnosis or exclusion of asthma based on the dose (PD20) or concentration (PC20) of inhaled methacholine that provokes a 20% decrease in the forced expiratory volume in 1 second (FEV1). However, since the American Thoracic Society (ATS) standards were published in 2000,1 the English Wright nebulizer (EW) recommended for the 2-minute tidal breathing method has become difficult to find; hence, many laboratories substitute other nebulizers with little standardization of the amount expected to deposit within the lungs.

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