The Test Sample
What is being tested?
Peritoneal fluid is a liquid that acts as a lubricant in the abdominal cavity. It is found in small quantities between the layers of the peritoneum. Produced by mesothelial cells in the abdominal membranes, peritoneal fluid acts to moisten the outside of the organs and to reduce the friction of organ movement during digestion.
A variety of conditions and diseases can cause inflammation of the peritoneum (peritonitis) and/or excessive accumulation of peritoneal fluid (peritoneal effusion or ascites). Peritoneal fluid analysis is a group of tests that evaluate this liquid to determine the cause of the increased fluid.
The two main reasons that fluid may collect in the abdominal cavity are:
- An imbalance between the pressure within blood vessels—which drives fluid out of blood vessels—and the amount of protein in blood—which keeps fluid in blood vessels. The fluid that accumulates in this case is called a transudate. Transudates are most often caused by congestive heart failure or cirrhosis.
- An injury or inflammation of the peritoneum, in which case the fluid is called an exudate. This type of fluid may be the result of conditions such as infection, malignancies (metastatic cancer, lymphoma, mesothelioma), or autoimmune disease.
Differentiation between the types of fluid is important because it helps diagnose the likely cause of fluid accumulation. Doctors and laboratorians use an initial set of tests (cell count, albumin level, and appearance of the fluid) to distinguish between transudates and exudates. Once the fluid is determined to be one or the other, additional tests may be performed to further pinpoint the disease or condition causing ascites.
How is the sample collected for testing?
A sample of peritoneal fluid is collected by a doctor with a syringe and needle using a procedure called paracentesis.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
You will be asked to empty your bladder prior to sample collection.