Thoracentesis yields straw-colored fluid

A 67-year-old man comes to the physician because of a 2-month history of progressive shortness of breath. He has had a 4.5-kg (10-lb) weight loss over the past 4 months. He has not had chest pain. He has congestive heart failure treated with furosemide, digoxin, and enalapril. He has smoked two packs of cigarettes daily for 30 years. He appears alert and is in no acute distress. His temperature is 37.2 C (99 F), blood pressure is 140/85 mm Hg, pulse is 84/min, and respirations are 18/min. Examination shows no jugular venous distention. There is dullness to percussion, and breath sounds are decreased at the left base. Cardiac examination shows a laterally displaced point of maximal impulse, normal S1 and S2, and an S3 at the apex. There is 1+ edema over the extremities. An x-ray film of the chest shows an enlarged cardiac silhouette, left hilar fullness, and a moderate-sized left pleural effusion. Thoracentesis yields straw-colored fluid.

Laboratory studies show:

Serum
Glucose 90 mg/dL
Protein 7 g/dL
Lactate dehydrogenase 300 U/L
Pleural fluid
pH 7.25
Glucose 75 mg/dL
Protein 4.5 g/dL
Lactate dehydrogenase 280 U/L
Leukocyte count 2000/mm3
Segmented neutrophils 15%
Lymphocytes 85%

A Gram's stain and acid-fast stains are negative for any organisms.
Which of the following is the most likely cause of this patient's pleural
effusion?

A ) Bacterial pneumonia

B ) Collagen vascular disease

C ) Congestive heart failure

D ) Malignancy

E ) Pulmonary embolus with infarction

F ) Viral pleuritis

D