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Relationship of Allergic Degree and PC20 Level in Adults with Positive Methacholine Challenge Test

Background: The relationship between allergic markers and PC20 (provocative concentration causing a 20% fall in FEV1) in adults with positive methacholine challenge test (MCT) is still subject to discussion. Objective: The goal of this study is to determine whether the degree of bronchial hyperresponsiveness (BHR) is correlated with the severity of atopy or not. Methods: Forty patients with persistent cough and/or unexplained episodes of dyspnea exhibiting a normal baseline pulmonary function test and positive MCT were enrolled in this study. They were divided into two groups according to their Phadiatop response (positive and negative), and three groups by PC20 level: PC20 < 1.25 mg/ml, 1.25 mg/ml ≤ PC20 < 5 mg/ml, and 5 mg/ml ≤ PC20 < 25 mg/ml. Results: Twenty-three patients (57.5%) were Phadiatop positive. Of the 23 Phadiatop-positive patients, 20 patients (87%) were positive for specific serum IgE to Dermatophagoides pteronyssinus (D1) and Dermatophagoides farinae (D2). The total serum IgE and eosinophil cationic protein (ECP) level of the Phadiatop-positive group were higher than those of the Phadiatop-negative group (p < 0.0001 and p = 0.005, respectively). The age, gender, FEV1/FVC ratio, ECP and total serum IgE level were not significantly different in the three PC20 subgroups. The Phadiatop response and PC20 level were significantly correlated (p = 0.0063). For Phadiatop-positive adults, PC20 level was not significantly correlated with total serum IgE and specific serum IgE to D1 and D2. Conclusion: Atopy is related to adults with positive MCT. However, the degree of BHR to methacholine is not significantly correlated with the severity of atopy.