The criteria for a complicated<unk>  include Gram stain–positive or culture-positive pleural fluid, pleural fluid pH <7.20, and pleural fluid LDH that is greater than three times the upper limit of normal of serum LDH. Diagnostic techniques available include plain film chest x-ray, computed tomography (CT), and ultrasound. Ultrasound can be useful in differentiating between empyema and other transudative and exudative effusions due in part to relative echogenicity of different organs such as the liver (often isoechogenic with empyema).
Parapneumonic effusion
Pleurisy
Pleural empyema
Pulmonary consolidation
Pleural effusion
Malignant pleural effusion
Pulmonary infiltrate
Subpulmonic effusion