In this blog, we will look into methacholine challenge test and its importance and assessment of bronchial asthma.
Bronchial asthma is a reversible airway disease where there is an increase in FEV1 of 12% and increase of 200ml post bronchodilator in a pulmonary function test. The same may be true for FVC (force vital capacity).
In many situations there is a question if someone currently has asthma or not. Methacholine challenge test may help in assessing if somebody does not have asthma, especially if the methacholine challenge test negative. It has a negative predicted value; meaning, if the test is negative then the chances of having underlying bronchial asthma would be less likely. If the test is positive, it does not mean that the person has asthma and it may be other conditions like postnasal drip, gastroesophageal reflux disease, sinus congestion, etc., that may give a falsely positive methacholine challenge test.
Methacholine challenge test is performed in increasing concentrations of challenge with methacholine and if the highest concentration of 16 mg/ml does not show any bronchospasm then the underlying likelihood of bronchial asthma would be less likely.
Chronic asthma symptoms may be evaluated with methacholine and if the methacholine test is negative then it would make underlying bronchial asthma less likely although the person may be experiencing asthma-like symptoms and it could be related to other symptoms like postnasal drip or gastroesophageal reflux disease. A complete pulmonary function test needs to be performed or at least a spirometry with and without bronchodilator needs to be performed prior to the assessment of methacholine challenge test.
In summary, methacholine challenge test is an important test assessment of bronchial asthma and if there is a question of presence of an asthma or not, a negative methacholine challenge test may help in ruling out underlying bronchial asthma. The positive methacholine challenge test needs to be clinically assessed for the likelihood of underlying bronchial asthma.