Pleural Effusions

Pleural effusions have traditionally been classified as transudative versus exudative and thoracentesis with application of Light’s Criteria used to differentiate the two with 98% sensitivity and 83% specificity for exudative process.

Pleural Fluid Analysis

Is it a pleural exudate?

The diagnosis of an exudate is most accurate if cholesterol in the pleural fluid is greater than 55 mg/dL (LR range, 7.1-250), lactate dehydrogenase (LDH) is greater than 200 U/L (LR, 18; 95% CI, 6.8-46), or the ratio of pleural fluid cholesterol to serum cholesterol is greater than 0.3 (LR, 14; 95% CI, 5.5-38). A diagnosis of exudate is less likely when all Light’s criteria (a ratio of pleural fluid protein to serum protein >0.5, a ratio of pleural fluid LDH to serum LDH >0.6, or pleural fluid LDH >two-thirds the upper limit of normal for serum LDH) are absent (LR, 0.04; 95% CI, 0.02-0.11).

Hydropneumothorax in a post pneumonectomy patient

Hydropneumothorax in a post pneumonectomy patient. Note the perfectly horizontal fluid line due to a true air-fluid interface rather than a fluid meniscus that would be typical of a pleural effusion in the absence of a pneumothorax. Also note the volume loss on the effected side rather than positive mass effect consistent with the lung having been removed.

TB or not TB…that is the question

Does this patient have an exudative pleural effusion? The Rational Clinical Examination systematic review.

Wilcox ME, Chong CA, Stanbrook MB, Tricco AC, Wong C, Straus SE.

JAMA. 2014 Jun 18;311(23):2422-31. doi: 10.1001/jama.2014.5552.

“The diagnosis of an exudate was most accurate if cholesterol in the pleural fluid was greater than 55 mg/dL (LR range, 7.1-250), lactate dehydrogenase (LDH) was greater than 200 U/L (LR, 18; 95% CI, 6.8-46), or the ratio of pleural fluid cholesterol to serum cholesterol was greater than 0.3 (LR, 14; 95% CI, 5.5-38). A diagnosis of exudate was less likely when all Light’s criteria (a ratio of pleural fluid protein to serum protein >0.5, a ratio of pleural fluid LDH to serum LDH >0.6, or pleural fluid LDH >two-thirds the upper limit of normal for serum LDH) were absent (LR, 0.04; 95% CI, 0.02-0.11).”