Which statement about transudative pleural effusions is true?

• A. Increased capillary permeability
• B. Normal capillary integrity
• C. Local pleural infection
• D. Pleural hemorrhage

Answer: (B)

Transudative pleural effusions occur when systemic forces alter the balance of fluid movement across the pleural membranes without damaging the capillary walls. The capillary integrity being normal means the vessels aren’t leaking due to inflammation; instead, fluid leaks because of increased hydrostatic pressure (as in congestive heart failure) or decreased oncotic pressure (as in hypoalbuminemia from cirrhosis or nephrotic syndrome). That’s why this statement fits transudates best. In contrast, exudative effusions arise from inflammation or infection that makes capillaries more permeable, so they contain more protein and LDH and are often associated with pleural infection, malignancy, or inflammatory conditions. Pleural hemorrhage and local infection describe non-transudative processes driven by inflammation or bleeding, not by normal capillary integrity.