A 64-year-old woman is found to have a left- sided pleural effusion on chest x-ray. Analysis of the pleural fluid reveals a ratio of concentration of total protein in pleural fluid to serum of 0.38, a lactate dehydrogenase (LDH) level of 125 IU, and a ratio of LDH concentration in pleural fluid to serum of 0.46. Which of the following disorders is most likely in this patient?

(Braunwald, 15/e, p 1513.) Classifying a pleural effusion as either a transudate or an exudate is useful in identifying the underlying disorder. Pleural fluid is exudative if it has any one of the following three propeies: a ratio of concentration of total protein in pleural fluid to serum greater than 0.5, an absolute value of LDH greater than 200 IU, or a ratio of LDH concentration in pleural fluid to serum greater than 0.6. Causes of exudative effusions include malignancy, pulmonary embolism, pneumonia, tuberculosis, abdominal disease, collagen vascular diseases, uremia, Dressler syndrome, and chylothorax. Exudative effusions may also be drug- induced. If none of the aforementioned propeies are met, the effusion is a transudate. Differential diagnosis includes congestive hea failure, nephrotic syndrome, cirrhosis, Meigs syndrome (benign ovarian neoplasm with effusion), and hydronephrosis.