Utility and efficiency of methacholine challenge testing in evaluating pediatric asthma: unraveling the diagnostic...

Interpretation of methacholine challenge testing (MCT) results depends on the patient's pretest probability of asthma as well as the provocative concentration (PC₂₀); however, ordering providers rarely understand the complexity associated with its interpretation. This study investigated the clinical utility and efficiency of MCT at a tertiary center in evaluating pediatric asthma.

Retrospective chart review was done for all MCT done at a tertiary center over a six year period (2011-2017). Demographics, referring provider, referral diagnosis, current symptoms with and without exercise, and baseline spirometry were collected. Pretest probability of asthma was assigned by author (RB) who was blinded to MCT results and PC₂₀. Post-test probability of asthma was assigned based on pretest probability, MCT result (+/-), and PC₂₀. Three assigned asthma probability categories were "unlikely" "likely", and "very likely".

Of 172 subjects (91 Females, age range 5-21 years), 64.9% of MCT results (n = 111)) were negative and 35.1% (n = 60)) were positive. One was inconclusive. Those who tested positive were shorter, lighter, younger and had lower forced expiratory volume in one second/forced vital capacity (FEV₁/FVC) ratio than those who tested negative (p < 0.05). Subjects with exercise symptoms only were less likely to test positive (OR 0.2, CI 0.1-0.5). In a majority of subjects (91.8%; 157/171), MCT increased the certainty of presence or absence of asthma.

In our subject population, MCT could be useful in evaluating pediatric asthma if subject's pretest probability of asthma and PC₂₀ was taken into account. It was not as useful for subjects with exercise symptoms only.