This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
Finding the cause of ascites
Ascites is fluid that builds up in the abdomen. About 80% of cases in Western countries are due to cirrhosis, but heart failure, cancer, tuberculosis, pancreatitis and kidney disease can also cause it. A diagnostic tap (paracentesis) followed by simple tests on the fluid usually points to the cause.
The serum-ascites albumin gradient
SAAG = serum albumin − ascitic fluid albumin
Both values should be measured on the same day. The gradient reflects the pressure in the portal vein: high pressure pushes fluid out of the blood vessels while albumin, a large molecule, stays behind.
- 1.1 g/dL (11 g/L) or more: portal hypertension is present, usually from cirrhosis, alcoholic hepatitis, heart failure, Budd-Chiari syndrome or massive liver metastases.
- Below 1.1 g/dL: portal hypertension is unlikely; think of peritoneal cancer, tuberculosis, pancreatitis, bowel perforation or nephrotic syndrome.
In a landmark 1992 study, Bruce Runyon and colleagues showed that the gradient classified ascites correctly in about 97% of cases, much better than the old exudate/transudate rule based on protein alone.
Adding the ascitic protein
| SAAG | Ascitic protein | Typical causes |
|---|---|---|
| High | below 2.5 g/dL | Cirrhosis, late Budd-Chiari |
| High | 2.5 g/dL or more | Heart failure, early Budd-Chiari |
| Low | 2.5 g/dL or more | Peritoneal cancer, tuberculosis, pancreatic ascites |
| Low | below 2.5 g/dL | Nephrotic syndrome |
Example
Serum albumin 3.0 g/dL and ascitic albumin 1.0 g/dL give a SAAG of 2.0 g/dL. With ascitic protein at 1.5 g/dL, the pattern fits cirrhosis. A neutrophil count of 100 cells/mm³ does not suggest infection.
Infection of the fluid
Spontaneous bacterial peritonitis is a serious infection of ascitic fluid without an obvious source. A neutrophil count of 250 cells/mm³ or more is enough to start antibiotics, even before culture results. Patients with low ascitic protein, below about 1.5 g/dL, are at higher risk and may receive preventive antibiotics.
Practical points
The gradient stays valid after diuretics in most cases. Very low serum albumin can make the gradient falsely low, and high serum globulins can make it slightly unreliable. Other tests on the fluid, such as cell count, culture, cytology, amylase and triglycerides, complete the picture depending on the suspected cause.