Radiographs can be helpful but are often normal.
CBC may or may not show eosinophilia. Transtracheal wash may show eosinophils, but this is also not pathognomonic for asthma. Bronchoscopy usually reveals mucosal erythema and edema and significant circumferential reduction in airway lumens. Peribronchial cuffing is usually found. The diaphragm may be flattened and the lung fields may appear hyperlucent, both indicating air trapping.