Ancillary examinations: (1) Radiological examinations: A routine chest X-ray should be performed in children with chronic cough, and the next diagnostic treatment or examination should be decided based on whether the chest X-ray is normal or not. A cavitation is taken when sinusitis is suspected or further consultation at the Department of Otolaryngology is recommended. CT of the chest helps to detect small and medium-sized lesions in the mediastinum, hilar lymph nodes and lung fields, while high-resolution CT helps to diagnose atypical bronchiectasis, interstitial lung disease, etc. CT sinus films showing thickening of the nasal mucosa >4 mm or air-fluid flat or fuzzy opacity in the sinus cavity are characteristic changes of sinusitis. CT and MRI of the sinus region is one of the indispensable diagnostic tools, but it should not be included as a routine test and can be performed at the discretion of the doctor depending on the condition. The results should be interpreted with caution in children, especially in children under 1 year of age, because the sinuses are not well developed (maxillary and septal sinuses are present at birth but small, frontal and pterygoid sinuses appear only at 5-6 years of age) and the structure is not clear, so imaging alone can easily lead to an overdiagnosis of “sinusitis”. (2) Pulmonary function: Pulmonary ventilation function tests should be routinely performed in children over 5 years of age, and if necessary, further bronchodilatation tests or bronchial excitation tests can be performed according to the exertional expiratory volume in one second (FEVl) to assist in the diagnosis of asthma (including CVA) and the differentiation from EB. (3) Bronchoscopy (fiberoptic bronchoscopy, rigid bronchoscopy, etc.): Bronchoscopy is feasible for chronic cough caused by suspected airway developmental malformations, foreign bodies (including airway endogenous foreign bodies and sputum plugs), and when anti-pollution pathogenic microbial examination is required. (4) Induced sputum or bronchoalveolar lavage fluid cytology and isolated culture of pathogenic microorganisms: can clarify or suggest respiratory tract infection pathogens, and if eosinophils are elevated, it is a major indicator for the diagnosis of allergic inflammatory diseases such as EB. (5) Others: PPD skin test, serum total IgE and specific IgE determination, skin prick test (SPT), 24-hour esophageal pH monitoring, esophageal luminal impedance test, etc. In contrast, the diagnostic value of exhaled breath nitric oxide assay, tracheobronchial biopsy, and cough receptor sensitivity testing for chronic cough in children is uncertain.