Safety of the Methacholine Challenge Test in Patients with Severe Airway Obstruction

Airway hyperresponsiveness (AHR) is defined as an increased sensitivity to bronchoconstrictor stimuli. It is regarded as the physiological hallmark of bronchial asthma. The methacholine challenge test has proved to be helpful in the diagnosis of asthma and the evaluation of AHR. The aim of this study was to investigate the safety of the methacholine challenge test among patients with low FEV1, who posed a substantial risk for deterioration of airway obstruction. We retrospectively investigated 241 asthmatic patients who had an initial FEV1 less than 1L and who underwent a methacholine challenge test (initial FEV1: 0.77±0.15L, 38.8±11.6% of predicted value; PC20: 3.1±4.6 mg/ml). Among the 241 asthmatic patients with FEV1＜1L, 108 (44.8%) had full post-challenge reversibility after b2 agonist inhalation. In contrast, only 58 controls with FEV1＞1L (22%) had significant postchallenge reversibility. The degree of post-challenge reversibility in asthmatic patients with FEV1＜ 1L was significantly inversely correlated with the initial FEV1 and the end FEV1 after a methacholine challenge. There were no major respiratory complications related to the methacholine challenge test. Thus, the methacholine challenge test is relatively safe but potentially dangerous in patients with severe airway obstruction. The patient’s condition should be monitored closely during the test, and a bronchodilator should be used to reverse the airway obstruction related to the methacholine challenge.