Paracentesis is a procedure that removes fluid buildup from your abdomen using a needle. The fluid, called ascites, can accumulate in the space between your abdominal organs for a variety of reasons, most commonly liver cirrhosis. Doctors perform paracentesis both to figure out why the fluid is there and to relieve the discomfort it causes.
Why Fluid Builds Up in the Abdomen
Your abdomen contains a thin membrane called the peritoneum that lines the organs and the abdominal wall. Normally, only a small amount of fluid exists in this space. When disease disrupts the body’s fluid balance, liters of fluid can accumulate, causing the abdomen to swell, feel tight, and press on the lungs.
Cirrhosis is the most common cause. Scarring in the liver raises pressure in the main vein feeding into it (portal hypertension), which forces fluid out of blood vessels and into the abdominal cavity. Other causes include heart failure, liver failure, and cancers of the ovary, colon, stomach, pancreas, or liver. Sometimes the fluid itself becomes infected, a condition called spontaneous bacterial peritonitis, which can be life-threatening if not caught quickly.
Diagnostic vs. Therapeutic Paracentesis
There are two distinct reasons for the procedure, and sometimes both happen during the same session.
Diagnostic paracentesis is a small-volume tap, typically removing just 30 to 50 milliliters of fluid for lab testing. It’s used when ascites appears for the first time and the cause isn’t clear, or when someone with known ascites develops worrisome symptoms like fever, abdominal pain, confusion, low blood pressure, or signs of worsening liver or kidney function. The goal is to identify what’s causing the fluid or to check for infection.
Therapeutic paracentesis is about symptom relief. When ascites becomes severe, often called “tense ascites,” it can make it hard to breathe, eat, or move comfortably. If water pills (diuretics) and a low-sodium diet haven’t controlled the fluid, a large-volume drain can remove several liters at once. The improvement in comfort and breathing is often immediate and significant.
What Happens During the Procedure
Paracentesis is done at the bedside, not in an operating room. You’ll be asked to empty your bladder first, since a full bladder sits close to the insertion area and could be accidentally punctured. You’re then positioned in bed with your head raised 45 to 90 degrees. If the doctor plans to insert the needle on your left side, you may be rolled partially onto that side so the fluid pools in one area and the air-filled loops of bowel float upward, out of the way.
The doctor selects an insertion site, usually either the midline of the abdomen about two centimeters below the navel, or a spot on the lower left side of the abdomen. Ultrasound is often used to confirm where fluid has collected and to make sure no bowel is sitting underneath the planned entry point. The skin is cleaned and numbed with a local anesthetic.
A needle is then inserted slowly through the abdominal wall. There’s typically a slight “pop” sensation when it passes through the peritoneal membrane and reaches the fluid. For a diagnostic tap, a syringe draws out a small sample. For a therapeutic drain, a flexible catheter is threaded over the needle, the needle is removed, and the catheter is connected to tubing that feeds into collection bags or vacuum bottles. The fluid drains by gravity, and the process can take 20 to 45 minutes depending on how much needs to come out.
What the Fluid Tells Your Doctor
Ascitic fluid goes through several tests that help pinpoint the cause and detect complications. One of the most useful is the serum-ascites albumin gradient, or SAAG. This compares a protein called albumin in your blood to the albumin level in the ascitic fluid. If the difference is 1.1 grams per deciliter or higher, portal hypertension is almost certainly the cause, with a sensitivity of 97% and specificity above 90%. A gap below 1.1 points toward other causes like cancer, tuberculosis, or pancreatic disease.
The fluid is also tested for infection. A white blood cell count with a specific threshold matters here: if a type of immune cell called a neutrophil reaches 250 or more cells per cubic millimeter, that’s the diagnostic hallmark of spontaneous bacterial peritonitis, even before culture results come back. This is why a diagnostic tap is so important when someone with ascites shows any sign of infection. Early detection can be the difference between a course of antibiotics and a medical emergency.
Additional tests may include fluid cultures (placed directly into blood culture bottles at the bedside for the best accuracy), total protein levels, glucose, and, when cancer is suspected, a check for abnormal cells.
Large-Volume Drainage and Albumin Replacement
When therapeutic paracentesis removes a large amount of fluid, the body can respond poorly. Pulling liters of protein-rich fluid out of the abdomen shifts the body’s fluid balance and can drop blood pressure. To counter this, doctors give intravenous albumin (a protein solution) based on how much fluid is removed. Standard protocols call for 25 grams of albumin when 5 to 6 liters are drained, 50 grams for 7 to 10 liters, and 75 grams for anything above 10 liters. It’s not unusual for people with advanced liver disease to have 10 or more liters of fluid drained in a single session.
Risks and Complications
Paracentesis is considered quite safe. The overall complication rate is approximately 1%. The most common issues are fluid leaking from the puncture site after the needle is removed, minor bleeding, and local infection. Serious complications like significant internal bleeding or bowel perforation are rare.
When bleeding complications do occur, about half are abdominal wall hematomas (bruising in the tissue layers of the belly wall), roughly 40% involve bleeding inside the abdominal cavity, and a small percentage involve damage to a blood vessel near the puncture site. Ultrasound guidance and careful site selection, particularly avoiding surgical scars and visible veins, help minimize these risks.
What Recovery Looks Like
A diagnostic tap is quick, and most people feel no different afterward aside from mild soreness at the puncture site. Therapeutic drainage brings more noticeable relief: the abdominal tightness eases, breathing feels easier, and appetite often improves within hours. A small bandage covers the insertion site, and you’ll typically be monitored briefly before going home or returning to your hospital room.
For people with chronic conditions like cirrhosis, paracentesis is often a recurring procedure. Ascites tends to reaccumulate over days to weeks when the underlying cause hasn’t been resolved, so repeat drainage sessions become part of ongoing management. Some people come in every one to two weeks for large-volume taps, a routine that, while inconvenient, offers consistent relief from the pressure and discomfort of tense ascites.