ascites
Meaning of ascites: Comparing the albumin in the fluid against the albumin in blood sorts the possible causes into two groups more reliably than symptoms do.
Definition of ascites
Ascites is an abnormal build-up of fluid in the peritoneal cavity, the space surrounding the organs of the abdomen. A small volume is normally present there. When far more collects, the abdomen swells visibly, clothing tightens, and weight rises without any change in what is being eaten. Advanced liver disease is the most common cause.
How does fluid come to collect there?
The peritoneal cavity is a closed space lined by a thin membrane that normally holds only a film of lubricating fluid. Fluid gathers when it is pushed out of blood vessels faster than it can be reabsorbed, or when the lining itself produces it. In cirrhosis both happen at once. Scarring inside the liver obstructs blood arriving from the intestines, so pressure rises in the portal vein, a state called portal hypertension, and that pressure forces fluid out of the vessels. Meanwhile the damaged liver makes less albumin, the blood protein whose osmotic pull keeps fluid inside vessels, so less is drawn back. Hormonal signals then instruct the kidneys to hold on to salt and water, adding further volume to the system.
What else causes it?
| Cause | Mechanism |
|---|---|
| Cirrhosis of the liver | Portal hypertension together with low blood albumin |
| Congestive heart failure | Backward pressure through the veins draining the abdomen |
| Cancer involving the peritoneal lining | Fluid produced by tumor deposits on the membrane |
| Infection of the lining | Inflammation making the membrane leak |
| Kidney disease with heavy protein loss | Low blood albumin without portal hypertension |
Malignant ascites is the term used when tumor is the source, and its fluid differs in composition from the fluid of liver disease.
How is the fluid analyzed?
Fluid is withdrawn through a needle inserted into the abdomen, a procedure called paracentesis, which both relieves pressure and supplies a sample. The single most useful measurement compares the albumin concentration in the fluid against the albumin in blood drawn at the same time. A wide gap between the two indicates portal hypertension and points toward the liver or the heart. A narrow gap points instead to the lining itself as the source, as in cancer or infection. Cell counts, bacterial culture and examination for tumor cells refine the answer further, and a raised white cell count within the fluid indicates infection of the fluid itself even when the abdomen is not tender to touch.
Used in a sentence
Paracentesis was performed to relieve the patient's ascites and to send the fluid for laboratory analysis.
Good to know
Comparing the albumin level of the ascitic fluid against that of the blood helps distinguish ascites caused by portal hypertension from liver disease from ascites arising from other causes such as infection or cancer.
Word origin
Where “ascites” comes from
From Greek askites, derived from askos, meaning a leather bag or wineskin.