Which condition accounts for the majority of transudative pleural effusions?

• A. Chronic infection
• B. Heart failure
• C. Pneumonia
• D. Pulmonary embolism

Answer: (B)

Transudative pleural effusions arise from systemic imbalances that push fluid into the pleural space rather than from local pleural inflammation. The fluid is typically low in protein and LDH. The most common cause is heart failure, where increased hydrostatic pressure in the pulmonary vasculature—often from left-sided (and sometimes combined with right-sided) heart failure—drives fluid out into the pleural space. This results in clear, protein-poor fluid and is frequently bilateral, reflecting overall venous congestion. In contrast, infections like pneumonia or chronic infection cause exudates from inflammation and increased vascular permeability, while pulmonary embolism can also produce exudates. Thus heart failure best explains the majority of transudative pleural effusions.