A 50-year-old man presents with pleuritic chest pain and breathlessness. Pleural fluid analysis: protein 4.8 g/dL, serum protein 7.2 g/dL, LDH 380 U/L (serum LDH 290 U/L), glucose 3.1 mmol/L, pH 7.18, WBC 18,000 (90% neutrophils). What do Light's criteria indicate, and what additional finding mandates immediate chest tube drainage?
- A Transudate by Light's criteria; no drainage needed
- B Exudate by Light's criteria; pH < 7.2 and low glucose indicate a complicated parapneumonic effusion/empyema requiring immediate chest tube drainage ✓
- C Exudate by Light's criteria; observation alone is appropriate pending culture results
- D Indeterminate by Light's criteria; repeat aspiration in 48 hours
Correct answer: B. Exudate by Light's criteria; pH < 7.2 and low glucose indicate a complicated parapneumonic effusion/empyema requiring immediate chest tube drainage
Explanation
Light's criteria identify an exudate when at least one of: pleural/serum protein ratio > 0.5 (4.8/7.2 = 0.67), pleural/serum LDH ratio > 0.6 (380/290 = 1.31), or pleural LDH > 2/3 upper limit of normal. This fluid fulfils two criteria. Pleural pH < 7.2 and glucose < 3.3 mmol/L in this context indicate a complicated parapneumonic effusion or empyema, mandating immediate chest tube drainage per BTS guidelines.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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