To help diagnose the cause of peritonitis and/or peritoneal fluid accumulation (ascites)
Peritoneal Fluid Analysis
When a doctor suspects that someone with abdominal pain and swelling, nausea, and/or fever has a condition associated with inflammation of the peritoneum (peritonitis) or peritoneal fluid accumulation
A peritoneal fluid sample obtained by inserting a needle into the abdominal cavity
You will be asked to empty your bladder prior to sample collection.
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How is it used?
Peritoneal fluid analysis is used to help diagnose the cause of peritoneal fluid accumulation (ascites) and/or inflammation of the peritoneum (peritonitis). There are two main reasons for fluid accumulation and an initial set of tests (protein or albumin, cell count and appearance) is used to differentiate between the two types of fluid that may be produced (exudate and transudate).
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When is it requested?
Peritoneal fluid analysis may be requested when a doctor suspects that a patient has a condition or disease that is causing peritonitis and/or ascites. It may be used when a patient has:
- Ascites of unknown origin
- Abdominal pain and tenderness
- Intestinal perforation
- Suspected intra-abdominal malignancy
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What does the test result mean?
An initial set of tests performed on a sample of peritoneal fluid helps determine whether the fluid is a transudate or exudate. This differentiation is mainly based on protein content of the fluid. Protein concentration is high in exudative ascites and low in transudative ascites but, sometime there is an overlap. The gradient between blood albumin concentration and ascitic fluid albumin concentration (SAAG) has 97% accuracy.
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Is there anything else I should know?
The gross appearance of the fluid can provide useful diagnostic information. In cirrhosis, the fluid usually has a clear straw-coloured appearance. A blood-stained sample is usually due to a traumatic tap and in these cases the fluid tends to clot on standing. Samples which remain homogeneously blood stained throughout the tap could indicate malignancy, pancreatitis, TB, intestinal infarction or recent abdominal trauma.
Ascitic fluid amylase is diagnostic of ascites secondary to pancreatic disease. Therefore, this is usually performed in patients with suspected pancreatic disease. High neutrophil count (type of white blood cells) >250 cells/mm³ is diagnostic of spontaneous bacterial peritonitis. The concentration of red blood cells is usually lower than 1000 cells/mm³ in ascitic fluid.
Cytology examination of ascitic fluid can help diagnose malignant causes of ascites. Gram staining of ascitic fluid is usually not indicated as it is very rarely helpful. Ascitic fluid culture for mycobacteria has about 50% sensitivity of diagnosis.
To help identification of organism in infections, it is useful to culture ascitic fluid in blood culture inoculation bottles.
Other tests: Lactate dehydrogenase activity and tumour markers are tested in certain malignancies causing ascites. Adenosine deaminase activity is checked in ascites caused by tuberculosis.
Glucose level in ascitic fluid usually reflects prevailing blood levels unless it is used by bacteria and white blood cells in ascitic fluid. Therefore, decreased glucose levels may support tuberculous or bacterial peritonitis and ascites due to malignancies.
If a doctor suspects that a patient may have a systemic infection, then a blood culture may be requested in addition to the peritoneal fluid analysis.
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What is paracentesis and how is it performed?
Paracentesis is the removal of peritoneal fluid from the abdominal cavity with a needle, tubing, and a container that may have a vacuum. The patient is positioned lying down with the head of the bed raised. A local anaesthetic is applied and then the doctor inserts the needle into the abdominal cavity and the sample is removed.
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Are there other reasons to do a paracentesis?
Yes. Sometimes it will be performed to drain excess peritoneal fluid – to relieve pressure in the abdomen. The volume of fluid removed may be large – sometimes as much as four litres (1 gallon) or more. This may need to be repeated periodically with some diseases. Laboratory testing of fluid in this situation is not required.
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Are any other procedures done to help evaluate conditions involving the peritoneum?
Yes. If abdominal bleeding is suspected but is not evident because there is no swelling of the abdomen, a peritoneal lavage may be performed. This is done by inserting a small tube (catheter) into the peritoneal space, infusing a small amount of sterile fluid, and then withdrawing the fluid to see if any blood is present. A cell count is usually performed on a sample of the fluid. This is rarely performed now with the availability of CT scanning.