A pleural fluid analysis shows: protein 4.8 g/dL (serum 6.9), LDH 420 U/L (serum 180), pH 7.18, glucose 42 mg/dL, ADA 60 U/L, negative Gram stain. What is the most likely diagnosis and the next best step?

• A Tuberculous pleurisy; start anti-TB therapy with closed-tube drainage
• B Malignant effusion; cytological examination
• C Rheumatoid pleurisy; systemic steroids
• D Complicated parapneumonic effusion/empyema; chest tube drainage ✓

Explanation

This is an exudative effusion (Light's criteria: pleural/serum protein ratio 0.69, pleural/serum LDH ratio 2.33) with very low pH (<7.20), low glucose, and high LDH — characteristics of a complicated parapneumonic effusion or empyema requiring immediate chest tube drainage. Light's criteria for complicated effusion: pH <7.20, glucose <60 mg/dL, LDH >1000 U/L. Tuberculous effusion characteristically has ADA >40 U/L but pH is usually >7.30 and glucose is not this low. This profile most urgently requires drainage, not just anti-TB therapy.

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

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Written and medically reviewed by the StethoPrep medical team.