About the SAAG Calculator – Serum-Ascites Albumin Gradient
The serum-ascites albumin gradient (SAAG) is a simple subtraction that helps classify the cause of ascites — fluid buildup in the abdominal cavity. It replaced the older exudate/transudate model because it is grounded in the physiology of portal pressure rather than a fixed protein cutoff. The gradient is calculated from a blood sample and a sample of ascitic fluid drawn on the same day.
How the gradient is calculated
SAAG equals the serum albumin concentration minus the ascitic fluid albumin concentration, with both values reported in g/dL:
- SAAG = Serum albumin − Ascitic fluid albumin
- Both samples should be drawn close together in time, ideally the same day, since albumin levels can shift with hydration and treatment.
- The ascitic fluid total protein is not part of the SAAG formula itself, but it is commonly checked alongside it to further narrow the differential within the high-gradient group.
Interpreting the gradient
A SAAG of 1.1 g/dL or higher indicates portal hypertension, correctly classifying the cause in about 97% of cases in the original validation studies. Common high-gradient causes include cirrhosis, alcoholic hepatitis, cardiac ascites, Budd-Chiari syndrome, and massive liver metastases. A SAAG below 1.1 g/dL points away from portal hypertension, toward causes such as peritoneal carcinomatosis, tuberculous peritonitis, pancreatic ascites, biliary ascites, and nephrotic syndrome.
Within the high-gradient group, the ascitic fluid total protein helps separate the underlying mechanism further: a protein below 2.5 g/dL is typical of cirrhosis, alcoholic hepatitis, and other primary liver disease, while a protein of 2.5 g/dL or higher is more typical of cardiac ascites, constrictive pericarditis, or early Budd-Chiari syndrome, where hepatic sinusoidal pressure rises without loss of liver synthetic function.
When to consult a professional
This tool performs the standard SAAG subtraction and reports the conventional interpretation bands; it does not diagnose the cause of ascites on its own. Paracentesis, fluid analysis, and the gradient result should be reviewed together by the clinician managing the case, alongside cell count, culture, cytology, and the patient's overall clinical picture.