Peritoneal fluid analysis is also known as paracentesis or an abdominal tap. It’s a procedure that tests the fluid collected from the peritoneal space. Doctors recommend this analysis when an abnormal amount of fluid collects in the peritoneal space. The peritoneal space is part of the abdomen that contains the gastrointestinal organs.

A doctor withdraws the fluid by numbing the skin (with local anesthetic) and inserting a long, thin needle into the peritoneal space. The fluid drains into collection containers. The doctor sends these containers to a laboratory to undergo a series of tests. The results of these tests help your doctor reach a diagnosis and decide on the best treatment plan for you.

The most common reason for performing peritoneal fluid analysis is to determine why an unusual amount of fluid is building up in the abdomen.

Peritoneal fluid analysis is also the test doctors use to diagnose peritonitis, a potentially fatal bacterial or fungal infection of the lining of the inner abdominal wall. Trauma teams may use this procedure to quickly check for internal bleeding in patients with abdominal trauma.

Finally, peritoneal fluid analysis can be a comfort measure to remove large amounts of fluid from the abdomens of people who have liver failure or advanced cancer.

A doctor in either an inpatient or an outpatient setting can perform peritoneal fluid analysis. Before the procedure, you’ll remove your clothes and change into a hospital gown.

You can sit up during the test if your doctor plans to remove only a small amount of fluid. If the doctor anticipates withdrawing a large amount of fluid, you will lie on your back with your head slightly elevated.

The doctor then cleans the area of the abdomen where they’ll insert the needle. The antiseptic may feel cold against your skin, but it won’t hurt. After cleaning the skin, the doctor will drape your abdomen with a sterile covering.

The doctor will then inject a small amount of local anesthetic into the skin. You’ll feel a needle prick, and the injection itself will sting. However, the discomfort doesn’t last long because your skin will go numb.

After your skin is numb, the doctor injects a long, hollow needle into the peritoneal area and pulls back on the plunger, drawing the fluid out of your abdomen. You may feel a dull pain or pressure during this procedure. If the doctor withdraws a large amount of fluid, you may feel dizzy and light-headed. If this happens, tell the doctor immediately.

It’s important to remain as still as possible until the test is over. Peritoneal fluid analysis takes around 30 to 45 minutes and may involve the removal of more than a gallon of fluid from the peritoneal area.

After the procedure, the doctor will apply a bandage or small surgical dressing to the puncture site. You may notice a small amount of clear drainage from the site for the next two to three days.

The doctor then checks your vital signs and monitors your blood pressure for a short time to make sure it doesn’t drop unexpectedly.

Unless your doctor tells you otherwise, you should be able to return to all of your usual activities after the test.

Call your doctor or return to the hospital immediately if you:

  • develop a temperature over 100°F
  • experience severe abdominal pain, tenderness, or redness
  • notice heavy bleeding or discharge at the puncture site

The laboratory technicians perform many tests on the peritoneal fluid. They check the general appearance to see whether it’s clear, red-tinged, or milky-white. They will most likely test for albumin and protein levels, and do a count of red and white blood cells in the sample.

They also test the sample for bacteria or fungi, which could be the cause of an infection. Finally, the technicians look at the size and shape of the cells—a practice known as cytology—to see if any of the cells show changes that could indicate cancer.

There are a few results that doctors are quick to notice:

  • bile-stained fluid, which indicates gallbladder or liver disease
  • pink or red fluid, which implies internal bleeding
  • a large difference between amount of albumin in peritoneal fluid and amount of albumin in blood, which suggests failure of the heart, liver, or kidneys
  • increased white cell count, which indicates an inflammation or infection (peritonitis)
  • increased protein in the sample, which could indicate liver disease or cancer

The preliminary results take less than a day to process. Once your doctor receives them, they’ll make treatment suggestions or possibly recommend a round of more specialized tests to address the organ that appears to be the cause of your problem.

Peritoneal fluid analysis is known as a safe procedure. The most common negative outcome is low blood pressure, which occurs after removing a large amount of fluid from the body. Administering rapid intravenous (IV) fluids can treat this.

Other potential risks include damage to the surrounding organs, and infection or prolonged bleeding at the puncture site.