What it is (overview)

Paracentesis with imaging guidance is a diagnostic procedure used to remove a sample of fluid from the abdominal cavity (the space around the organs) when fluid has built up there. This fluid buildup is called ascites and may cause abdominal swelling, discomfort, or trouble breathing. During paracentesis, a clinician places a thin needle (or small catheter) through the skin of the abdomen to withdraw fluid. Using imaging guidance—most often ultrasound, and sometimes a CT scan—helps the provider choose the safest spot, avoid blood vessels and organs, and improve the success of the procedure, especially when the fluid is in small pockets.

The fluid removed (“ascitic fluid”) is sent to a laboratory for testing. Common measurements include:

• Cell count and differential (looks for inflammation or infection).
• Albumin and total protein (helps determine why fluid is accumulating, such as liver-related portal hypertension vs other causes).
• Culture and Gram stain (checks for bacterial infection).
• Cytology (looks for cancer cells).
• Other targeted tests as needed (e.g., amylase for pancreatic causes, triglycerides for chylous ascites, tests for tuberculosis).

In plain language, results help answer questions like: “Is the abdominal fluid infected?”, “Is it most likely related to liver disease?”, “Could cancer be causing the fluid accumulation?”, or “Is there another condition triggering the swelling?” A normal result depends on why the test was done, but in general, no evidence of infection (low white blood cells and negative culture) and no cancer cells on cytology are reassuring. Abnormal findings may point to infection (such as spontaneous bacterial peritonitis), malignancy, pancreatitis-related leakage, kidney or heart-related fluid overload, or other inflammatory conditions.

When & why it's usually done

Doctors commonly order paracentesis with ultrasound or CT guidance when a person has new or worsening abdominal fluid accumulation or unexplained abdominal swelling. It may be recommended for diagnosis, symptom relief, or both. Imaging guidance is especially helpful when fluid is hard to locate by exam alone, when the abdomen is very tense, or when a patient has had prior surgery or scarring.

This test is usually done to:

• Find the cause of ascites (new-onset fluid or fluid that is getting worse).
• Check for infection in abdominal fluid, particularly in people with cirrhosis or known ascites (urgent if there is fever, abdominal pain, confusion, low blood pressure, kidney problems, or worsening illness).
• Evaluate for cancer when there is unexplained weight loss, known malignancy, or imaging that suggests tumor-related fluid.
• Assess complications of liver disease (for example, portal hypertension leading to ascites).
• Relieve symptoms such as pain, tightness, poor appetite, nausea, or shortness of breath caused by severe fluid buildup (therapeutic paracentesis may remove a larger volume).

Common reasons someone might need this diagnostic procedure include persistent belly bloating, rapid increase in waist size, discomfort when lying flat, swelling in the legs along with abdominal distention, abnormal liver tests, known cirrhosis, or concerning findings on ultrasound/CT that show fluid in the abdomen.

Common diseases related to it

• Cirrhosis and complications of chronic liver disease (portal hypertension–related ascites)
• Spontaneous bacterial peritonitis (SBP) and other abdominal fluid infections
• Peritoneal carcinomatosis (cancer spread to the lining of the abdomen)
• Ovarian, gastrointestinal (stomach/colon), pancreatic, or liver cancers associated with ascites
• Congestive heart failure (fluid overload–related ascites)
• Kidney disease, including nephrotic syndrome
• Pancreatitis or pancreatic duct leak (enzyme-rich ascites)
• Tuberculous peritonitis (abdominal tuberculosis)
• Inflammatory or autoimmune conditions affecting the peritoneum (less common)

Health goals where it may help

• Diagnosing the cause of abdominal swelling and confirming whether ascites is present
• Monitoring and managing liver health in chronic liver disease and cirrhosis
• Early detection of abdominal infection to reduce complications and hospitalization risk
• Guiding cancer evaluation when malignancy-related fluid accumulation is suspected
• Improving comfort and breathing by relieving pressure from severe fluid buildup (therapeutic drainage)
• Supporting treatment planning by tailoring therapy based on fluid test results (e.g., antibiotics, diuretics, oncology care)