Blood tests showed a hemoglobin concentration of 12.6 g/dL; lactate dehydrogenase, 514 U/L; total protein, 5.4 g/dL; and albumin, 3.1 g/dL. Renal panel, electrolyte levels, coagulation panel, and thyroid-stimulating hormone levels were unremarkable. A plain chest radiograph (Fig 2) and chest CT scan (Fig 3) revealed massive left-sided effusion with contralateral shift of the mediastinum. Pleural thickening, pleural mass, or mediastinal adenopathy was absent. Therapeutic, left-sided thoracentesis revealed straw-colored nonhemorrhagic exudative effusion with a total protein concentration of 3.8 g/L and lactate dehydrogenase concentration of 277 U/L. Pleural fluid pH was 7.27; WBC count, 4,910 cells/mL; RBC count, 19,690 cells/mL; neutrophils, 5%; lymphocytes, 88%; monocytes, 7%; and mesothelial cells, moderate. Pleural fluid cytology was negative for malignant cells. The results of Gram stain, acid-fast bacilli, and cultures were negative. The results of HIV and rapid plasmin reagin serology were negative. Paraphenylenediamine was nonreactive.