Proulx F, et al. - Given that in order to shorten the testing time of methacholine challenge test for asthma diagnosis, protocols that quadruple methacholine concentrations are extensively practiced among adults but have not been assessed in children for the same purpose, therefore, researchers inquired clinical predictors related to the preclusion of a quadrupled concentration protocol in children. A derivation cohort comprising individuals < 18 years who underwent methacholine challenge tests between April 2016 to February 2017; and a validation cohort including those who performed these tests from March 2017 to September 2017, were included. The eligibility of a participant to omit the 0.5 mg/ml and 2.0 mg/ml concentrations on the basis of their PC₂₀ was determined. The factors that significantly precluded the omission of the 0.5 mg/ml concentration were: a baseline forced expiratory volume in 1 s (FEV₁) ≤ 90% predicted, FEV₁/forced vital capacity ≤ 0.8, forced expiratory flow at 25–75% of the pulmonary volume (FEF_25-75) ≤ 70% predicted, and a reduction in FEV₁ ≥ 10% with the previous concentration, and those that significantly precluded the omission of the 2.0 mg/ml concentration were: a baseline FEF_25-75 ≤ 70% predicted and a reduction in FEV₁ ≥ 10% with the previous concentration. The overall sensitivity of 74.0% and specificity of 84.6% was obtained by applying these 4 criteria to the validation cohort. The objective pulmonary function measures that are revealed in this study may personalize as well as shorten the methacholine challenge protocol in children by quadrupling concentrations.