Transudative pleural effusions are most commonly associated with which condition?

• A. Chronic infection
• B. Heart failure
• C. Malignancy
• D. Pneumonia

Answer: (B)

Transudative pleural effusions occur when systemic factors alter fluid balance across the pleural membranes, leading to fluid leakage that has low protein and low LDH. The key idea is that these effusions reflect changes in hydrostatic or oncotic pressures rather than local inflammation of the pleura. The most common cause is congestive heart failure, where elevated hydrostatic pressure in the pulmonary circulation pushes fluid into the pleural space, often producing bilateral effusions. While other conditions like cirrhosis or nephrotic syndrome can also cause transudates by lowering oncotic pressure, heart failure remains the most frequent association. In contrast, exudative effusions stem from local pleural disease (infection, malignancy, pneumonia) and typically have higher protein and LDH.