Paracentesis is a treatment for patients with ascites, which is the medical terminology for abdominal fluid buildup. Such buildup may occur as a result of trauma, infections, inflammation, liver disease or cancer. Here, a long, narrow needle is employed through the abdomen to remove some of the fluid so that it can be sent to a lab for testing. When necessary, a larger portion of the fluid can be removed to alleviate pain or pressure on the pelvic organs. By examining a sample of the fluid under a microscope, a pathologist may be able to determine why the fluid is present and look for signs of cancer. The procedure can be done with the patient in a sitting position except in cases where a large volume of fluid is to be retrieved – in which case the patient will be lying down. After administering a numbing medication into the belly, the physician carefully inserts the paracentesis needle into the location of the fluid; in some cases, this may be done with the assistance of ultrasound imaging. Patients need to keep still during the procedure except as otherwise instructed.