Bronchial methacholine challenge is well established in asthma diagnostics and research. ATS guidelines propose a five step standard dosimeter (SDM) protocol with incremental concentrations of methacholine to calculate the concentration causing a 20% drop in FEV₁ in an individual (PC₂₀FEV₁). In contrast, the aerosol provocation system (APS) by Viasys^® automatically determines the administered dose of methacholine by measuring the effective nebulisation time and referring it to drug concentration and nebuliser power. Therefore, it offers a feasible and less time-consuming provocation procedure by applying incremental doses (PD₂₀) of methacholine using a single concentration (16mg/mL methacholine, APS-SC). In this study we compared these two methods in 52 young adults (25±5.8 years). Following a screening visit, subjects were randomly assigned to undergo either SDM or APS-SC followed by the other method within 1 week. A close correlation between concentration and dosage causing a 20% fall of FEV₁ was found (r=0.69, p<0.001).

Using the ATS categorisation of bronchial responsiveness we interpreted the results of the APS-SC method as follows: PD₂₀ methacholine<0.3mg as “moderate to severe BHR”, 0.3 – 0.6mg as “mild BHR”, 0.6 – 1.0mg as “borderline BHR”, and>1.0mg as “normal bronchial response”.

We conclude that the five-step APS-SC is a suitable method, providing reliable results. In clinical practice the APS-SC is a timesaving procedure and less prone to errors since only one dilution of methacholine is necessary compared to the SDM.