A 65-year-old man with right-sided exudative pleural effusion (LDH 380 U/L, protein 4.8 g/dL, glucose 28 mg/dL, pH 7.12) is suspected to have a complicated parapneumonic effusion. Which characteristic definitively indicates the need for chest tube drainage?

• A LDH >200 IU/L
• B Exudative nature by Light's criteria
• C Pleural fluid pH <7.20 ✓
• D Glucose <60 mg/dL

Explanation

Pleural fluid pH <7.20 is the single most important criterion mandating drainage in parapneumonic effusions — it correlates with bacterial invasion and fibrin deposition. The BTS guideline threshold for drainage is pH <7.20 (with a 30-minute blood gas analyzer measurement, not dipstick pH). Low glucose alone (<60 mg/dL) and high LDH are supportive features but not absolute indicators. Empyema (frank pus) also mandates drainage regardless of pH. Large free-flowing effusions on the same side as pneumonia may not need drainage if pH >7.30. Frank empyema, positive culture, or loculation are additional independent indications.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.