This study was a multicenter, open, observational study and was divided into two stages; Stage I study includes patients with suspected asthma to observe the diagnostic value and safety of Methacholine Choline Provocation Test. All patients clinically evaluated for bronchial provocation testing were included in the stage II study to further validate the diagnostic value and cutoff value of the methacholine choline provocation test.

This study was a multicenter, open, observational study. The study was divided into two stages; the first stage of the study included a population with suspected asthma and performed a bronchial provocation test, and cumulative provocation dose when forced expiratory volume in one second (FEV1) fell by 20% (PD20 ) data were recorded. Subjects with positive excitation were treated as asthma for 3 months and treatment was considered effective to confirm the diagnosis of asthma. Sensitivity, specificity, and reliability of the methacholine choline provocation test were calculated, and cutoff values were obtained by exploratory analysis based on PD20 values. All patients clinically evaluated for bronchial provocation testing were included in the stage II study to further validate the diagnostic value and cutoff value of the methacholine choline provocation test.

Inclusion Criteria:

Stage I study:

• clinically evaluated as suspected asthma but have not been previously diagnosed as asthma and require a bronchial provocation test
• Basal lung function FEV1 ≥ 60%
• Meet the requirements for conducting bronchial excitation tests and pulmonary ventilation examinations
• Not currently suffering from or accompanied by other respiratory diseases, including allergic rhinitis, chronic obstructive pulmonary disease, chronic bronchitis, etc.

Stage II study:

• Basal lung function FEV1 ≥ 60%
• Meet the requirements for conducting bronchial excitation tests and pulmonary ventilation examinations

Exclusion Criteria:

• Have had a fatal asthma attack, or have required mechanical ventilation for an asthma attack within the last 3 months
• Definite hypersensitivity reaction to inhaled stimulants or salbutamol or unexplained urticaria
• Severe impairment of basal pulmonary ventilation (FEV1 < 60% of expected value %, or < 1 L in adults)
• Poor cooperation with basal pulmonary function tests that do not meet quality control requirements
• Other conditions that make a bronchial provocation test or pulmonary ventilation function test inappropriate (e.g., recent presence of severe cardiovascular disease, seizures, uncontrolled hypertension, etc.)

Stage I study: patients with one or more symptoms such as wheezing, shortness of breath, cough and chest tightness, clinically evaluated as suspected asthma but not previously diagnosed as asthma and requiring bronchial provocation test, such as patients with suspected asthma without obstructive pulmonary function changes, patients with suspected cough variant asthma (CVA) in chronic cough, patients with recurrent chest tightness episodes suspected of chest tightness variant asthma (CTVA), etc.

Stage II study: bronchial provocation test is required after clinical evaluation, including patients with suspected asthma, asthma, allergic rhinitis, chronic obstructive pulmonary disease, and chronic bronchitis.