CHEST Guidelines-Methacholine-Challenge-Testing-in-the-Diagnosis-of

Methacholine-Challenge-Testing-in-the-Diagnosis-of

Pdf Summary

The Methacholine Challenge Test (MCT) is a direct bronchoprovocation test primarily utilized for diagnosing asthma in individuals with potential symptoms but normal or non-diagnostic spirometry results. This test measures airway hyperresponsiveness (AHR) by evaluating the response of airway smooth muscles. Two critical considerations include ensuring symptoms are current, ideally within a few days, and that methacholine is inhaled without deep inhalations, as these can affect test sensitivity.<br /><br />Cut points for the MCT are set to ensure high sensitivity and negative predictive value, with a Wright nebulizer tidal breathing (WTB) provocation concentration of 8 mg/mL indicating a fall of 20% in FEV1. A dose-based reporting method (PD20) is suggested for better comparability between different testing methods. MCT's diagnostic efficacy can be limited by the absence of a standard criterion for diagnosing asthma-related airway dysfunction in patients with non-diagnostic spirometry.<br /><br />Findings from a study by Selvanathan et al. evaluated the MCT in a cohort of asthma-diagnosed individuals with a negative bronchodilator response. Of these, 43% displayed a positive MCT, with additional cases converting upon medication adjustment or spontaneously. The negative predictive value of an 8 mg/mL cut point was 87.9%, increasing slightly with a 16 mg/mL cut point. In individuals with persistent negative MCTs, asthma was largely excluded, suggesting alternative symptom explanations.<br /><br />Key messages highlight that, despite underutilization and limited sensitivity, spirometry with bronchodilator testing should be supplemented with MCT in diagnosing asthma. A positive MCT supports AHR's presence, the physiological basis of asthma, while a negative MCT should prompt alternative diagnostics. Serial MCTs may be beneficial, especially when asthma symptoms persist but are infrequent or not recent. Additionally, avoiding deep inhalations during MCTs preserves sensitivity, and treatment efficacy can be indicated by MCT improvement.

Keywords

Methacholine Challenge Test

asthma diagnosis

airway hyperresponsiveness

spirometry

Wright nebulizer tidal breathing

FEV1

PD20

bronchodilator response

negative predictive value

serial MCTs