Diagnostic criteria for transudates and exudates

• Light's Criteria:  If at least one of the following three criteria is present, the fluid is virtually always an exudate; if none is present, the fluid is virtually always a transudate

  • Pleural fluid protein/serum protein ratio greater than 0.5.

  • Pleural fluid LDH/serum LDH ratio greater than 0.6.

  • Pleural fluid LDH greater than two thirds the upper limits of normal of the serum LDH.

• A meta-analysis involving 1448 patients in eight studies used receiver operating characteristic (ROC) analysis and found that three tests on a single pleural fluid sample could each discriminate as well between transudates and exudates as using paired and triplet combinations. An exudate in this study was best determined by any one of the following:
  

  • Pleural fluid protein >2.9 g/dL

  • Pleural fluid cholesterol >45 mg/dL

  • Pleural fluid LDH >45 percent of upper limits of normal serum value

Tables Adapted from ŠUpToDate7.2 1999