A pleural fluid analysis shows: protein 4.8 g/dL (serum protein 7.1 g/dL), LDH 320 IU/L (serum LDH 180 IU/L), pH 7.15, glucose 35 mg/dL, WBC 12000 with 90% neutrophils. Gram stain is negative. Using Light's criteria, this is an exudate. The LOW pH and glucose make this:

• A Simple parapneumonic effusion — treat with antibiotics alone
• B Rheumatoid pleurisy
• C Complicated parapneumonic effusion or empyema requiring chest tube drainage ✓
• D Malignant effusion

Explanation

Pleural fluid pH <7.2 and glucose <60 mg/dL in a parapneumonic effusion indicates a complicated effusion that will not resolve with antibiotics alone and requires chest tube drainage. These biochemical markers reflect anaerobic metabolism by pleural bacteria and neutrophils, indicating fibrin deposition beginning. If left undrained, it will progress to frank empyema (frank pus). Simple parapneumonic effusions have pH >7.3 and respond to antibiotics.

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

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Written and medically reviewed by the StethoPrep medical team.