QualityTest indicatedInterpretation
Appearance
BloodyHematocrit< 1 percent: nonsignificant
1 to 20 percent: cancer, pulmonary embolus, or trauma
> 50 percent peripheral hematocrit: hemothorax
Cloudy or turbidCentrifugationTurbid supernatant: chylothorax
Odor
PutridStain and culturePossible anaerobic infection
Distinguishing transudate from exudate
Light's criteriaFluid is exudate if it meets one or more of the following criteria:

  • Ratio of pleural fluid protein level to serum protein level > 0.5

  • Ratio of pleural fluid LDH level to serum LDH level > 0.6

  • Pleural fluid LDH level > two thirds the upper limit of normal for serum LDH level

Confirmation of Light's criteria assessment*Fluid is exudate if:

  • Serum albumin level - pleural fluid albumin level ≤ 1.2 g per dL (12 g per L)