June 27, 2010

MRCP 2 Question 4

A 65 year old smoker with a three month history of a dry cough develops bilateral pleural effusions. Thoracocentesis reveals a pleural effusion with a Lactic Acid Dehydrogenase level which is is less than 50% of the serum Lactic Acid Dehydrogenase level.

This suggests that:

a) the patient is probably diabetic
b) the patient is likely to have an empyema
c) the protein content of the effusion is likely to be above 4 g/dl
d) the specific gravity of the fluid is likely to be less than 1.02
e) the patient is likely to have a bronchogenic neoplasm




ANSWER
The correct answer is D


Explanation

A Pleural fluid LDH-to-serum LDH ratio <0.6 is suggestive of a transudate.
1. Laboratory differentiation.
§ Specific gravity. Under 1.016 is suggestive of a transudate.
§ Protein. Less than 3 g/dl is suggestive of a transudate.
§ Pleural fluid protein-to-serum protein ratio. <0.5 is suggestive of a transudate.
§ Pleural fluid LDH-to-serum LDH ratio. <0.6 is suggestive of a transudate.

The pleural fluid level is not useful in the differential diagnosis of exudative pleural effusion.

Nevertheless, it is recommended that a pleural fluid LDH level be measured every time a diagnostic thoracentesis is performed, since the level of LDH in the pleural fluid is a good indicator of the degree of inflammation in the pleural space.

If the pleural fluid LDH level increases with serial thoracentesis, the degree of inflammation is worsening and one should be more aggressive in pursuing the diagnosis

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