Review Question - QID 109189

The patient in this vignette presents with dyspnea, tachypnea, dullness to percussion, radiographic blunting of the costophrenic angle, and lab values suggestive of an exudative effusion, which could be caused by a pulmonary embolism.

Pleural effusions represent accumulations of fluid in the pleural space. Effusions are classified depending on their underlying etiology as either transudative (due to increased pulmonary capillary wedge pressure or decreased oncotic pressure) or exudative (due to increased vascular permeability). Light’s criteria can be used to differentiate transudative and exudative effusions. Per Light’s criteria, an effusion is exudative if it satisfies at least one of the following: pleural/serum protein ratio > 0.5, pleural/serum LDH > 0.6, or pleural LDH greater than 2/3 the normal upper limit for serum LDH.

Figure A demonstrates the characteristic appearance of a unilateral pleural effusion. Note the blunted costophrenic angle on the left.

Incorrect Answers:
Answers 2, 3, 4: Cirrhosis, nephrotic syndrome, and protein losing enteropathy can all cause transudative pleural effusions due to decreased oncotic pressure. The positive findings by Light's criteria mean this patient is more likely to have a exudative pleural effusion.

Answer 5: Congestive heart failure can cause transudative pleural effusions due to an increase of pulmonary capillary wedge pressure leading to buildup of fluid in the lungs. The positive findings by Light's criteria mean this patient is more likely to have a exudative pleural effusion.

Bullet Summary:
Light’s criteria suggest that a pleural effusion is likely to be exudative it has (1) pleural/serum protein ratio > 0.5, (2) pleural/serum LDH ratio > 0.6, or (3) pleural LDH that is > 2/3 the upper limit of normal serum LDH.