Laboratory Analysis of Peritoneal & Ascitic Fluid: Test Procedures and Significance

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Reasons

Our abdominal cavity and the organs within it are protected and lubricated by a fluid called the peritoneal or ascitic fluid. Usually there is a balance between secretion and absorption of fluid and the volume is small. However a variety of disease conditions can result in fluid build up of several litres (known as ascites).

The build up fluid is often visible from the resulting abdominal distension. Smaller volumes may only be visible radiologically. Due to its location this fluid can be drained or sampled relatively easily. A wide variety of laboratory tests can then be carried out on this fluid.

The Serum-Ascites Albumin Gradient (SAAG)

This imporant diagnostic test is calculated as the serum albumin minus the ascitic albumin. A blood test, in order to measure the albumin in the blood serum, is required in tandem with the peritoneal fluid analysis.

Ascites can be classiifed into transudates and exudates.Transudative ascites are defined as having a serum albumin-ascites gradient of more than 1.1 g/L and are usually caused by:

  • Liver cirrhosis
  • Congestive heart failure.
  • Hepatic vein obstruction (Budd Chiari syndrome) : commonly caused by tumors, hematologic disorders, infections, constrictive pericarditis, inferior vena cava obstruction, or viral hepatitis.

Exudative ascites are defined as having a Serum Albumin - Ascites gradient of less than 1.1 g/L and can be caused by:

  • Malignant diseases of the peritoneum
  • Tuberculous peritonitis
  • Pancreatitis (inflammation of the pancreas)
  • Post surgery starch powder peritonitis
  • Transected lymphatics following surgery
  • Sarcoidosis
  • Lymphatic obstruction
  • Amyloidosis
  • abdominal trauma
  • dialysis complications

Other Types of Peritoneal Fluid Analysis

As well as the serum-albumin-ascites gradient, other parameters can be assessed in peritoneal fluid analysis. These include:

  • Cell count: increased numbers of leukocytes (white blood cells) can be suggestive of infection.
  • Protein content: values of less than 1g/L suggests spontaneous peritonitis. Values of greater 1 g/L suggest secondary peritonitis.
  • Glucose content: values less than 50 mg/L is often seen in secondary peritonitis.
  • LDH (lactate dehydrogenase): above normal levels can indicate tissue damage.
  • Microbiology culture in order to identify bacterial infection in the fluid.
  • Cytology: to identify the presence of malignant cells. However, only certain types of cancer will show up in peritioneal fluid analysis.

Other Considerations

  • The results of peritoneal fluid analysis are only useful in diagnosis when taken together with a physical examination and understanding of the patients medical history.
  • There are disorders which can give the appearance of peritoneal fluid build up (i.e. a distended abdomen), which a clinician will be careful to exclude from their diagnosis, such as an ovarian cyst or obesity.
  • Treatment of ascites will depend on the underlying cause but can include drainage of the fluid, bed rest, low salt diet, reduced fluid intake and drug treatment.

References

Management of Ascites, F.Rochling & R.Zetterman, Drugs - Therapy in Practice. 2009, Vol 69, P1739-1760.