Paracentesis also.

Protein body fluid
Glucose body fluid
PH body fluid
Body fluid culture

A 60-year-old male with a right-sided pleural effusion undergoes thoracentesis.  Analysis of the pleural fluid reveals a protein level of 2.0 g/dL and an LDH level of 70 U/L.  His serum protein level is 7.0 g/dL (N 6.0-8.3) and his serum LDH level is 200 U/L (N 100-105). Based on these findings, which one of the following is the most likely diagnosis?  (check one)
 A. Heart failure 
 B. Pulmonary embolism 
 C. Tuberculous pleurisy 
 D. Malignancy 
 E. Bacterial pneumonia 

Pleural effusions may be exudates or transudates.  The distinction is important for an accurate diagnosis and to help determine what further evaluations may be necessary.  Lights criteria use ratios of fluid/serum values for protein and LDH.  Pleural fluid/serum ratios greater than 0.6 for LDH and 0.5 for protein are indicative of exudates.  In the scenario presented, both ratios are approximately 0.3; therefore, the fluid is a transudate. The list of causes for transudates is much shorter than for exudates.  The vast majority of transudates are due to heart failure, with cirrhosis being the next most common cause.  Once there is reasonable certainty that the fluid is a transudate, additional studies usually are not necessary.  The other conditions listed result in exudative pleural effusions. Ref: Porcel JM, Light RT: Diagnostic approach to pleural effusion in adults. Am Fam Physician 2006;73(7):1211-1220.