Peritoneal Fluid Analysis

• Physical characteristics—fluid appears clear
• Albumin level—decreased
• Cell count—few cells are counted

Transudates usually require no further testing. Ninety percent of ascitic fluids are transudates and are caused by either cirrhosis or congestive heart failure.

Exudate:

• Physical characteristics—fluid may appear cloudy
• Albumin level—higher than normal
• Cell count—increased

Exudates can be caused by a variety of conditions and diseases and usually require further testing to aid diagnosis. Exudates may be caused by, for example, infections, trauma, various cancers, or pancreatitis. The following is a list of additional tests that the doctor may order depending on the suspected cause:

Physical characteristics – the normal appearance of a sample of peritoneal fluid is straw coloured and clear. Abnormal appearances may give clues to conditions or diseases present and may include:

• Yellow with liver disease, milky from the lymphatic system, and greenish from bile
• Reddish peritoneal fluid may indicate the presence of blood
• Cloudy peritoneal fluid may indicate the presence of microorganisms and/or white blood cells pointing to an infection

Chemical tests – tests that may be performed in addition to albumin may include:

• Glucose - typically about the same as blood glucose levels. May be lower with infection.
• Amylase - increased with pancreatic disease
• Alkaline phosphatase - increased if intestines are damaged
• Tumour markers - to identify type of malignancy

Microscopic examination – may be performed if infection or cancer is suspected. Normal peritoneal fluid has small numbers of white blood cells (WBCs) but no red blood cells (RBCs) or microorganisms. Laboratories may examine drops of the peritoneal fluid and/or use a special centrifuge (cytocentrifuge) to concentrate the fluid’s cells at the bottom of a test tube. Samples are placed on a slide, treated with special stain, and an evaluation of the different kinds of cells present is performed.

• Total cell counts—quantity of WBCs and RBCs in the sample. Increased WBCs may be seen with infections and malignant conditions.
• WBC differential—determination of percentages of different types of WBCs. An increased number of neutrophils may be seen with bacterial infections.
• Cytology – a cytocentrifuged sample is treated with a special stain and examined under a microscope for abnormal cells and for white cell differentiation. The differential can help determine whether the cells are the result of an infection or the presence of a tumour.

Infectious disease tests – routine tests may be performed to look for microorganisms if infection is suspected:

• Gram stain - for direct observation of bacteria or fungi under a microscope. There should be no organisms present in peritoneal fluid.
• Bacterial culture and susceptibility testing - used to detect any microorganisms, which will grow in the culture. If bacteria are present, susceptibility testing can be performed to guide antimicrobial therapy. If there are no microorganisms present, it does not rule out an infection; they may be present in small numbers or their growth may be inhibited because of prior antibiotic therapy.

Other peritoneal fluid tests for infectious diseases that are less commonly used include tests for viruses, mycobacteria (AFB smear and culture), and parasites.