Light's criteria

Pleural effusion-->抽LDH, Protein

Exudative:
pleural fluid Protein/serum Protein > 0.5
pleural fluid LDH/LDH > 0.6
pleural fluid LDH > serum LDH 2/3 正常上限

sensitivity很高，negative-->「排除」, postive-->「不能確定」