A 55-year-old man presents with unilateral pleural effusion. Thoracentesis reveals: protein 4.8 g/dL, serum protein 7.2 g/dL (ratio 0.67), LDH 380 IU/L, serum LDH 180 IU/L (ratio 2.1). Glucose 35 mg/dL, pH 7.15. The most likely diagnosis is:
- A Transudative effusion (congestive heart failure)
- B Malignant pleural effusion
- C Complicated parapneumonic effusion or empyema ✓
- D Tuberculous pleural effusion
Explanation
Light's criteria confirm exudate: pleural/serum protein ratio >0.5 (0.67), pleural/serum LDH ratio >0.6 (2.1), pleural LDH >2/3 ULN. The critically low pH (<7.2) and glucose (<60 mg/dL) indicate a complicated parapneumonic effusion requiring chest tube drainage or empyema. These biochemical markers reflect high metabolic activity of neutrophils/bacteria consuming glucose and producing acid. A pH <7.0 indicates frank empyema needing surgical intervention (VATS decortication). Malignant effusions are exudates but typically have near-normal pH and glucose unless bulky disease. TB effusion has low glucose but pH is usually 7.2–7.3 and LDH/ADA ratio patterns differ. Transudates have neither criterion met.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.