- pleural fluid protein/serum protein >0.5
- pleural fluid LDH/serum LDH >0.6
- pleural fluid LDH more than two-thirds normal upper limit for serum
The above criteria misidentify approximately 25% of transudates as exudates. If one or more of the exudative criteria are met and the patient is clinically thought to have a condition producing a transudative effusion, the difference between the albumin levels in the serum and the pleural fluid should be measured. If this gradient is greater than 12 g/L (1.2 g/dL), the exudative categorization by the above criteria can be ignored because almost all such patients have a transudative pleural effusion.
If a patient has an exudative pleural effusion, the following tests on the pleural fluid should be obtained: description of the fluid, glucose level, differential cell count, microbiologic studies, and cytology.
- Light RW. Clinical practice. Pleural effusion. N Engl J Med. 2002 Jun 20;346(25):1971-7. [Medline]
Created: September 07, 2005