Critical Care Medicine-Pulmonary Disorders>>>>>Pleural Disorders
Question 1#

A 64-year-old female presents with a 5-day history of exertional dyspnea and orthopnea. Her medical history is significant for SLE and diastolic heart failure. Chest X-ray reveals significant bilateral pleural effusions. The decision is made to perform a thoracentesis.

Which laboratory value would indicate that the effusions are a result of her known diagnosis of SLE?

A. Pleural fluid to serum protein ratio less than 0.5
B. Pleural fluid LDH less than two-thirds the upper limit of normal serum LDH
C. Pleural fluid to serum LDH ratio greater than 0.6
D. Pleural fluid cholesterol less than 45 mg/dL

Correct Answer is C

Comment:

Correct Answer: C

When evaluating pleural fluid obtained from a thoracentesis, Light’s criteria can be used to differentiate a transudative effusion, which is due to an imbalance in hydrostatic and oncotic pressure, from an exudative effusion, which can be secondary to a myriad of alternative problems. A transudative effusion can be treated usually without undergoing the extent of investigation that is required if the effusion is exudative in origin. Transudative effusions tend to be seen in patients with known heart failure, nephrotic syndrome, and cirrhosis. Exudative effusions can be secondary to cancer, pneumonia, viral infections, TB, and pulmonary emboli. Exudative effusions result from a disruption in the capillary membrance, and the increased permeability leads to the leakage of cells, protein, and fluid into the pleural space. If one of the following is positive then the fluid is considered an exudate:

• Pleural fluid protein to serum protein ratio >0.5
• Pleural fluid LDH to serum LDH ratio >0.6
• Pleural fluid LDH > two-thirds the upper limit of normal serum LDH

Alternative criteria include the two-test and three-test rules. Only one criteria need be met for the fluid to be considered an exudate. Two-test rule:

• Pleural fluid cholesterol >45 mg/dL
• Pleural fluid LDH >0.45 times the upper limit of normal serum LDH

Three-test rule:

• Includes the above two criteria plus pleural fluid protein >2.9 g/dL

Reference:

1. Heffner JE, Brown LK, Barbieri CA. Diagnostic value of tests that discriminate between exudative and transudative pleural effusions. Chest. 1997;111(4):970.