Table 3.

Decision algorithm for suspected pleural infection based on pleural fluid analysis^a

Fluid appearance	Recommended approach
Purulent (i.e. frank pus)	Proceed to chest drain insertion (if safe to do so)
Non-purulent	Check pleural pH
	If ≤ 7.20	HIGH likelihood of infection → proceed to chest drain insertion
	If 7.21–7.39	INTERMEDIATE likelihood of infection → assess pleural LDH and glucose: 1. if LDH ≥ 900 IU/L and glucose ≤ 4 mmol/L, consider chest drain insertion (particularly if septations on TUS) 2. if LDH < 900 and glucose normal/high, no immediate indication for chest drain – continue to monitor clinically
	If ≥ 7.40	LOW likelihood of infection → no immediate indication for chest drain – continue to monitor clinically

LDH lactate dehydrogenase, TUS thoracic ultrasound

^aAdapted from British Thoracic Society guidelines, 2023 [4]