The Methacholine Challenge Test for Reversable Airways Disease Assessment: A Practical Guide on how to Interpret new 2017 ERS Guidelines
Jason A Suggett1, Mark W Nagel1 & Jolyon P Mitchell2
1Trudell Medical international, 725 Third Street, London, Ontario, N5V 5G4, Canada
2Jolyon Mitchell Inhaler Consulting Services Inc., 1154 St. Anthony Road, London, Ontario, N6H 2R1, Canada
The assessment through a challenge test of severity of reversible broncho-constrictive disease, such as asthma, is an important part of the diagnosis process as well as defining treatment therapy. Methacholine is frequently used as the inhaled challenge substance and is given by inhalation via a nebulizer for a fixed exposure time to the methacholine concentration. The challenge test involves progressively increasing the concentration of methacholine and measuring the forced expiratory volume in 1 s (FEV1) after exposure at each concentration level. The test is terminated after the first instance at which FEV1 decreases by more than 20% from the pre-test reference value. New recommendations from the European Respiratory Society (ERS) have recommended basing the result upon the delivered dose (µg) of methacholine causing a 20% fall in FEV1, termed the provocative dose (PD20), rather than the former metric of methacholine concentration (mg/mL), causing the same fall in FEV1 (PC20). Given the detail and complexity of the recent guidance, we follow a step-wise approach to explain each stage of the new bronchial challenge test, then illustrate how PD20 is calculated and used to interpret the degree of airway hyper-responsiveness. Although any nebulizer with validated methacholine delivery data could be used to deliver the agent, we illustrate how to apply the methodology, based on the same breath-actuated nebulizer (AeroEclipse-II* BAN) as was used, through references, in the new guidance.