Diagnosing ascites typically involves multiple tests, and your doctor may recommend specific procedures. Initially, a physical examination will be conducted to check for abdominal swelling, and blood tests may be ordered to measure protein levels in your blood. Additional imaging and diagnostic tests that may be used include:

Ultrasound

An abdominal ultrasound is a non-invasive test that uses sound waves to produce images of the organs within the abdomen. To ensure clear images, you may be asked to fast for 8 to 12 hours before the test to prevent undigested food from interfering with the sound waves. In the case of a liver or pancreas ultrasound, a fat-free meal the evening prior may be recommended. During the ultrasound, a handheld probe is moved across your abdomen, creating a digital image on a screen for the doctor to view. The procedure is painless and provides real-time images of abdominal organs and blood flow. Ultrasound can detect as little as 100 ml of ascitic fluid.

CT Scan

A CT scan, or computed tomography, is an advanced X-ray technique that provides cross-sectional images of the body. The scan revolves around the body and sends images to a computer for medical professionals to review. An abdominal CT scan allows doctors to examine the organs and blood vessels within the abdominal cavity. It provides detailed images that help in accurate diagnosis. You may be asked to fast for two to four hours prior to the scan, and in some cases, you may be instructed to drink water or contrast material for better visualization of the stomach and intestines.

MRI Scan

Magnetic resonance imaging (MRI) uses magnets and radio waves to create detailed images of the body’s internal structures. This non-invasive technique produces cross-sectional images of the abdomen, allowing doctors to identify any abnormalities within the tissues and organs. MRI does not use radiation and is considered a safer option compared to CT scans. During the procedure, you will lie on your back while the technician communicates with you through a microphone. The machine may produce loud noises, and it is important to remain still during the scan to avoid affecting the results.

Laparoscopy

Laparoscopy is a minimally invasive surgical procedure that allows doctors to examine the abdominal organs. A small incision is made, and a laparoscope—an instrument with a high-intensity light and camera—is inserted to provide real-time images of the inside of the abdomen. The procedure may also involve taking tissue samples if necessary. Laparoscopy is typically used when other diagnostic methods like CT or MRI scans are insufficient.

Fluid Sample (Diagnostic Paracentesis)

Your doctor may collect a sample of fluid from your abdomen using a needle. This fluid is then sent to the lab for analysis to identify any signs of infection or cancer, which can help determine the cause of ascites. Local anesthesia is given before the procedure to minimize discomfort. The fluid is tested for its appearance, protein level, albumin, and cell counts (both red and white). Additional tests, such as microbiological culture, Gram staining (for bacteria), and cytopathology (for cell and fluid examination), may also be performed.

The Serum Ascites Albumin Gradient (SAAG) is often more reliable than older methods for determining the cause of ascites. A high gradient (>1.1 g/dL) typically indicates ascites caused by portal hypertension, while a low gradient (<1.1 g/dL) suggests a non-portal hypertensive cause.

Classification of Ascites

Ascites can be categorized into three grades based on severity:

Grade 1: Mild, only visible via ultrasound or CT scan.
Grade 2: Noticeable with flank bulging and shifting dullness.
Grade 3: Easily visible and confirmed with the fluid wave or thrill test.