Ascites is a build-up of fluid in the peritoneal cavity – the space between the lining of the abdomen and abdominal organs. It can be caused by liver disease, various cancers, congestive heart failure, or kidney failure.
When portal hypertension develops as a result of liver cirrhosis, blood bypasses the liver and is diverted to abdominal peritoneal vessels. Then, due to increased capillary pressure, fluid leaks into the peritoneal cavity.
Mild ascites (defined as less than 400ml of fluid being present in an adult) is often without symptoms. As more fluid accumulates, abdominal distension, pain, discomfort, and bloating are frequently seen.
Ascites has traditionally been classed as either 'transudative' or 'exudative', based on the amount of protein found in the fluid. A more useful classification system, the Serum Ascites Albumin Gradient (SAAG), has since been developed based on the amount of albumin in the ascitic fluid compared to the amount of albumin in the blood.
The SAAG value for ascites caused by portal hypertension (cirrhosis or congestive heart failure for example) is generally more than 1.1; the value for ascites due to other causes (cancer or pancreatitis for example) is less than 1.1.
If more than 500ml of ascites fluid is present, it can be seen during physical examination as bulging and fluid waves as the doctor palpates the abdomen. Smaller amounts may be detected with an ultrasound scan of the abdomen, and are occasionally found by accident during an ultrasound or CT scan that is being performed for other reasons.
It is important to diagnose the underlying condition(s) that are causing ascites. Blood work is an essential tool and may include a complete metabolic panel and coagulation (clotting) panel.
Analysis of the fluid itself may be necessary. A needle is inserted into a sterilized area of the abdomen and a small sample of fluid is withdrawn.
A large accumulation of fluid may cause breathing difficulties by compressing the diaphragm and forming pleural effusion. Gut bacteria may invade the ascites (peritoneal) fluid and cause serious infection. Ascites related to cirrhosis may lead to progressive kidney failure.
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