MUC5AC and Pleural effusion: When MUC5AC level in sputum is more than 8,774 pg/mL, the LDH level in serum is more than 348 U/L, immunoglobulin IgM level is more than 3.39 g/L, NLR is more than 1.75, maximum temperature is more than 38.9°C, and the presence of pleural effusion, which will indicate the children need to be treated with fiberbronchoscopy.