A 70-year-old man presents with progressive dyspnea and pleuritic chest pain. Chest X-ray reveals a large left-sided pleural effusion. Thoracentesis is performed, and the fluid analysis shows a protein ratio of pleural fluid to serum >0.5, LDH ratio of pleural fluid to serum >0.6, and pleural fluid LDH >2/3 upper limit of normal serum LDH. Which of the following is the most likely etiology of his pleural effusion?
✓ Correct Answer: Option D
The fluid analysis meets Light's criteria for an exudative effusion (protein and LDH ratios are high). Among the options, pneumonia is a common cause of exudative pleural effusions. Other options typically cause transudative effusions.