A 65-year-old man with pleural effusion has the following pleural fluid analysis: protein 4.8 g/dL (serum protein 7.2 g/dL), LDH 380 U/L (serum LDH 240 U/L), glucose 42 mg/dL, pH 7.18. This pleural fluid profile is consistent with:
- A Uncomplicated parapneumonic effusion
- B Transudative effusion (heart failure)
- C Complicated parapneumonic effusion or empyema ✓
- D Chylothorax
Correct answer: C. Complicated parapneumonic effusion or empyema
Explanation
The pleural fluid/serum protein ratio (4.8/7.2 = 0.67 > 0.5) and LDH ratio (380/240 = 1.58 > 0.6) satisfy Light's criteria for exudate. The critically abnormal features — pH <7.20, glucose <60 mg/dL, and LDH >3× upper limit of normal — identify a complicated parapneumonic effusion or frank empyema requiring chest tube drainage. Uncomplicated parapneumonic effusion has pH >7.30 and glucose >60 mg/dL. Transudates have protein ratio <0.5 and LDH ratio <0.6.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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