Pleural fluid analysis in empyema typically shows which combination?

• A. pH > 7.20 and glucose > 60 mg/dL
• B. Leukocytosis with high protein
• C. pH < 7.20 and glucose < 60 mg/dL
• D. Low LDH

Answer: (C)

In empyema, the pleural space is infected and the fluid becomes an exudate with heavy neutrophil activity and bacterial metabolism. This environment drives two characteristic findings: the fluid becomes very acidic and glucose is consumed rapidly. A pH below 7.20 reflects acid production by both bacteria and inflammatory cells, while glucose under 60 mg/dL shows rapid consumption by these cells and bacteria. Together, these low values indicate a purulent, high-metabolic-state effusion that typically requires drainage plus antibiotics.

Leukocytosis with high protein can occur in many exudates and isn’t specific to empyema. A low LDH would be unusual for empyema, since inflammatory and infectious effusions often have high LDH due to cell turnover and damage. High pH or glucose preserved above these thresholds would point away from empyema and toward less severe parapneumonic effusion or a non-infected effusion. Therefore, the combination of pH < 7.20 and glucose < 60 mg/dL best characterizes empyema.