Thoracentesis: Results

A small amount of clear, colorless, or pale yellow pleural fluid, usually less than , is normally present. No infection, inflammation, or cancer is found.

A large amount of pleural fluid is present.

Fluid may be labeled as either a transudate or an exudate. The difference between these two types of fluid has to do with the amount of protein and other substances found in the fluid.

• A transudate has a low white blood cell (WBC) count, a low lactate dehydrogenase (LDH) enzyme level, and a low protein level. A transudate may be caused by cirrhosis, heart failure, or nephrotic syndrome.
• An exudate may be caused by diseases, such as infection (pneumonia), chest injury, cancer, pancreatitis, autoimmune disease, or a pulmonary embolism (PE).
  • If an infection is present, the exudate will have a high WBC count, a high LDH enzyme level, a high protein level, and bacteria or other infectious organisms.
  • If cancer is present, the exudate will have a high WBC count (often lymphocytes), a high LDH enzyme level, and a high protein level. Abnormal cells may also be present.
  • If a pulmonary embolism is present, the exudate will have a low WBC count and large numbers of red blood cells. The protein level for a PE may be high or low.