A n 84-year-old man presented to his local hospital after falling from his wheelchair. He had tachypnea and abdominal distention. Chest radiography revealed a rightsided pleural effusion, and abdominal radiography showed dilated loops of bowel, suggestive of bowel obstruction. The patient was then transferred to our hospital for further work-up.The patient reported worsening of shortness of breath and abdominal distention for the past few weeks. He had a 1-year history of early satiety, nausea, and dyspepsia but had noted no weight loss. The patient was taking omeprazole for peptic ulcer disease. Recently, after positive findings on a urea breath test, metronidazole and clarithromycin were initiated for treatment of Helicobacter pylori. The patient's medical history also included type 2 diabetes, benign prostatic hyperplasia, and hypertension for which he was taking aspirin, glipizide, lisinopril, and finasteride. He was a former smoker who had quit 50 years ago.Physical examination revealed the following: temperature, 36.4° C; blood pressure, 108/58 mm Hg; regular pulse rate, 103 beats/min; respiratory rate, 26 breaths/min; and oxygen saturation of 93% while breathing 3 L of oxygen. The patient was visibly tachypneic, with diffuse expiratory wheezing and decreased breath sounds in the right base. His abdomen was distended with bulging flanks and a positive fluid wave.Important laboratory values on admission included the following (reference ranges provided parenthetically): hemoglobin, 10.4 g/dL (13.5-17.5 g/dL); white blood cells, 12.2 x 10 9 /L (3.5-10.5 x 10 9 /L); platelets, 348 x 10 9 /L (150-450 x 10 9 /L); sodium, 134 mEq/L (135-145 mEq/L); bicarbonate, 21 mEq/L (22-29 mEq/L); blood urea nitrogen, 35 mg/dL (8-24 mg/dL); creatinine, 1.5 mg/dL (0.8-1.3 mg/ dL); chloride, 103 mmol/L (100-108 mmol/L); glucose, 160 mg/dL (70-100 mg/dL); aspartate aminotransferase, 15 U/L (17-59 U/L); total bilirubin, 0.3 mg/dL (0.1-1.0 mg/dL); albumin, 2.9 g/dL (3.5-5.0 g/dL); and lactate, 0.78 mmol/L (0.6-2.3 mmol/L).Abdominal computed tomography without contrast medium showed a moderate amount of ascites, moderate right-sided pleural effusion, and a mildly nodular configuration of the liver. Thoracentesis resulted in removal of 1 L of serosanguineous fluid. Pleural fluid lactate dehydrogenase (LDH) was 724 U/L, total protein was 4.1 g/dL, glucose was 121 mg/dL, and pH was 7.7. The total nucleated cell count was 1196 U/L, with differential of neutrophils at 46%, lymphocytes at 5%, monocytes at 2%, and eosinophils at 2%. The serum LDH level was 200 U/L, and the serum protein level, 5.7 g/dL. The first step in the evaluation of the pleural fluid is to determine whether it is a transudate or exudate. On the basis of criteria from Lights et al, 1 an exudate has a pleural fluid protein to serum protein ratio greater than 0.5, pleural fluid LDH to serum LDH greater than 0.6, or pleural fluid LDH greater than two-thirds the upper limit of the laboratory's normal serum LDH level. Fulfilling any of these 3 criteria indicates an exuda...