Paracentesis is a procedure that removes fluid buildup from inside your abdomen. The fluid, called ascites, accumulates in the space between your abdominal organs and can cause pain, bloating, a visibly swollen belly, and difficulty breathing. During paracentesis, a needle and a thin plastic tube (catheter) are inserted through your abdominal wall to drain this fluid, either to test it for a diagnosis or to relieve uncomfortable symptoms.
Why Paracentesis Is Performed
The procedure serves two distinct purposes, and which one applies to you determines how much fluid gets removed and what happens with it afterward.
Diagnostic paracentesis removes a small sample of fluid, typically collected in a few syringes, to figure out why fluid is building up in the first place. The lab tests run on this sample can identify infections, cancerous cells, and whether the fluid buildup is related to liver disease or something else entirely. This is especially important for detecting spontaneous bacterial peritonitis, a dangerous infection of the abdominal fluid that can develop in people with cirrhosis.
Therapeutic paracentesis drains a large volume of fluid to provide physical relief. When ascites becomes severe, your abdomen can feel painfully tight, and the upward pressure on your lungs can make it hard to breathe. Removing several liters of fluid can quickly ease abdominal pain, pressure, shortness of breath, bloating, and constipation. In some cases, both goals are accomplished in a single session: a sample is sent to the lab while the rest of the fluid is drained for comfort.
What Happens During the Procedure
Paracentesis is typically done at the bedside in a hospital or outpatient clinic. You’ll be asked to empty your bladder beforehand to reduce the risk of accidental injury during needle insertion. Most people are positioned lying on their back with the head of the bed slightly elevated, or turned partially onto one side to help fluid pool in a spot that’s easy to access.
The classic insertion site is in the lower left side of the abdomen. Your provider cleans the skin with an antiseptic solution and injects a local anesthetic to numb the area. A needle is then guided through the abdominal wall into the fluid-filled space. For a diagnostic tap, only about 20 to 60 milliliters is needed. For a therapeutic drain, a catheter is threaded through the needle and connected to a collection bag or vacuum bottles, and the fluid drains out over 20 to 60 minutes depending on how much is being removed.
The whole process is relatively quick. Most people describe feeling pressure rather than sharp pain once the area is numbed. After the needle or catheter is removed, a small bandage covers the puncture site.
The Role of Ultrasound Guidance
Traditionally, providers located the fluid by physical exam alone, tapping on the abdomen and listening for dullness. But research has shown this “blind” approach has an average success rate of only about 58%, and in some patients, air-filled loops of bowel sit directly in the expected needle path, raising the risk of injury. Ultrasound guidance lets the provider see exactly where the deepest pocket of fluid sits and confirm that no organs or blood vessels are in the way. This significantly improves both safety and the chance of successfully collecting fluid on the first attempt.
What the Fluid Reveals
When fluid is sent to the lab, one of the most useful tests is the serum-ascites albumin gradient, or SAAG. This compares the level of a protein called albumin in your blood to the level in the abdominal fluid. A difference of 1.1 grams per deciliter or higher points to portal hypertension, meaning elevated pressure in the blood vessels around the liver, which is the hallmark of cirrhosis-related ascites. A value below 1.1 suggests other causes, such as cancer, infection, or inflammation of the abdominal lining.
The fluid is also examined for white blood cell counts (to detect infection), total protein, and sometimes checked under a microscope for abnormal cells. Together, these results help narrow down the cause of fluid buildup and guide treatment decisions.
Risks and Complications
Paracentesis is considered a low-risk procedure. Large-volume paracentesis carries roughly a 1% risk of any complication, which may include leaking of fluid from the puncture site, localized infection, bleeding, or, very rarely, bowel perforation. Severe bleeding occurs in fewer than 0.2% of cases, and fatal hemorrhage is exceedingly rare, happening in less than 0.02%.
The most significant risk specific to large-volume drainage is called post-paracentesis circulatory dysfunction. When more than 5 liters of fluid are removed in a single session, the sudden shift in abdominal pressure can cause a drop in blood pressure and strain on the kidneys. To prevent this, providers give an intravenous albumin infusion during or immediately after the procedure when the volume drained exceeds that 5-liter threshold. This helps maintain blood volume and keeps circulation stable.
Recovery and What to Expect Afterward
Most people feel noticeably better within hours of a therapeutic paracentesis. The relief from abdominal tightness and improved breathing can be dramatic, especially if several liters were drained. You’ll typically be monitored briefly after the procedure, and the puncture site may ooze a small amount of fluid for a day or two, which is normal.
Keep the bandage clean and dry for at least 24 hours. Avoid heavy lifting or strenuous activity for a couple of days to give the puncture site time to heal. Watch for signs of infection at the site, such as increasing redness, warmth, swelling, or fever, and for any sudden increase in abdominal pain or dizziness, which could signal internal bleeding.
For people with chronic liver disease, ascites often reaccumulates over days to weeks. Repeat paracentesis is common, and some patients need the procedure every two to three weeks. Dietary sodium restriction and diuretic medications can help slow the rate of fluid return between procedures.