A 64-year-old woman is found to have a right-sided pleural effusion on chest x-ray. Analysis of the pleural fluid reveals pleural fluid to serum protein ratio of 0.38, a lactate dehydrogenase (LDH) level of 110 IU (normal 100-190), and pleural fluid to serum LDH ratio of 0.46. Which of the following disorders is most likely in this patient?a. Bronchogenic carcinoma
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 properties: a ratio of concentration of total protein in pleural fluid to serum greater than 0.5, an absolute LDH greater than 2/3 the upper normal in serum, or a ratio of LDH concentration in pleural fluid to serum greater than 0.6 (the “Light criteria”). Causes of exudative effusions include malignancy, pulmonary embolism, pneumonia, tuberculosis, abdominal disease, collagen vascular diseases, sarcoidosis, uremia, Dressler syndrome, and chylothorax. Exudative effusions may also be drug induced. If none of the aforementioned properties are met, the effusion is a transudate. Differential diagnosis for a transudative effusion includes congestive heart failure, nephrotic syndrome, cirrhosis, Meigs syndrome (benign ovarian neoplasm with effusion), and hydronephrosis. Exudative effusions are the result of an inflammatory process causing proteins to leak across the capillary membrane. Transudative effusions are caused by alterations in hydrostatic or oncotic pressures with normal capillary permeability.