How to check for asthma?

Asthma can be examined by sputum, and patients can find more eosinophils; chest X-ray examination can also be done, and early asthma can be found to increase the transparency of both lungs through X-ray examination; lung function examination can also be done, and when asthma attacks occur, the patient's forced expiratory volume in the first second and the maximum mid-expiratory flow rate are reduced.