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In pleural effusions associated with pneumonia, the presence of loculated pleural fluid, pleural fluid with a pH less than 7.20, pleural fluid with a glucose level less than 60 mg/dL (3.3 mmol/L), lactate dehydrogenase level greater than 1000 U/L, positive pleural fluid Gram stain or culture, or the presence of gross pus in the pleural space predicts a poor response to antibiotics alone; such effusions are treated with drainage of the fluid through a catheter or chest tube.
Tuberculous Pleural Effusion
A tuberculous effusion is typically exudative by both protein (pleural fluid to serum protein ratio greater than 0.5) and lactate dehydrogenase (LDH) criteria (pleural fluid to serum LDH ratio greater than 0.6 and pleural fluid to serum upper limits of normal LDH ratio greater than 0.6). The cellular response in the pleural fluid is classically lymphocytic (greater than 80% mature lymphocytes). However, it can be neutrophilic within the first 2 weeks, after which it typically evolves into the classic lymphocyte-predominant exudate. Whereas pleural fluid cultures for Mycobacterium are positive in less than one third of cases, the combination of pleural biopsy for histologic evaluation and culture is typically positive in more than two thirds of cases.
Malignancy is the most common cause of chylothorax, but trauma is the second most common cause. Chylothorax can also occur in association with pulmonary tuberculosis and chronic mediastinal infections, sarcoidosis, lymphangioleiomyomatosis, and radiation fibrosis.
pleural fluid in chylothorax is usually milky but may also be serous or serosanguineous in malnourished patients with little fat intake. The pleural fluid triglyceride concentration in a chylothorax is typically greater than 110 mg/dL (1.24 mmol/L) and occurs in association with a low pleural fluid cholesterol concentration. If the pleural fluid triglyceride level is less than 50 mg/dL (0.6 mmol/L), chylothorax is unlikely.