Table 1. Parapneumonic effusion classification.

Anatomy	Bacteriology	Chemistry	Category	Drainage intervention
Very small to small free flowing effusion*	Unknown	Unknown	1	No
Small to moderate free flowing effusion*	Negative culture and Gram stain	Normal pH and glucose	2	No
Large effusion or loculation*	Positive culture or Gram stain	Low pH or glucose	3	Yes
Any size	Pus		4	Yes

*, small <10 mm on lateral decubitus; moderate less than half hemithorax; large greater than or equal to half hemithorax. Risk of poor outcome is very low to low for category 1 and 2; however category 3 and 4 have moderate to high risk.