Hepatology
SAAG (Ascites)
Serum–ascites albumin gradient.
Education and reference only. Not a substitute for clinical judgement, local policy or product labelling. Always verify before clinical use. Values are calculated in your browser and never stored.
Background
The serum–ascites albumin gradient (SAAG) classifies the cause of ascites by subtracting the ascitic-fluid albumin from the serum albumin measured on the same day. It is based on oncotic and hydrostatic principles: a high gradient reflects the raised portal pressure that drives fluid out of the circulation. The SAAG has replaced the older transudate/exudate classification because it more reliably distinguishes portal-hypertensive from non-portal causes. The result is reported in g/dL.
Interpreting the result
A gradient of 1.1 g/dL or more indicates portal hypertension, such as cirrhosis or heart failure, and does so with high accuracy. A gradient below 1.1 g/dL points to a non-portal cause such as peritoneal malignancy, tuberculosis or pancreatic ascites. The cut-off is robust but identifies the mechanism rather than the specific diagnosis, so it is interpreted alongside cytology, culture and other fluid studies.
Worked example
A patient with a serum albumin of 3.5 g/dL and an ascitic albumin of 1.0 g/dL has a SAAG of 2.5 g/dL. Being well above 1.1 g/dL, this indicates portal hypertension as the cause, consistent with cirrhosis.
Critical actions
Use g/dL (divide g/L by 10) and samples taken the same day. A gradient ≥1.1 g/dL indicates portal hypertension with ~97% accuracy.
Pearls / pitfalls
- Use albumin in g/dL (divide a g/L result by 10) and take both samples on the same day.
- A high gradient does not exclude a second cause — a patient with cirrhosis can also develop, for example, malignant or infected ascites.
- Very low serum albumin can narrow the gradient slightly, but the 1.1 g/dL threshold remains reliable.
- The SAAG identifies the mechanism, not the diagnosis; always pair it with cell count, cytology and culture.
Evidence & validation
Validated by Runyon and colleagues, who showed the gradient correctly classified the cause of ascites in around 97% of cases, outperforming the exudate–transudate approach. It is endorsed in hepatology guidance on the diagnostic evaluation of ascites.
Frequently asked questions
What does a SAAG of 1.1 g/dL or more mean?
It indicates that the ascites is due to portal hypertension, such as cirrhosis or heart failure, with about 97% accuracy. A value below 1.1 g/dL points to a non-portal cause.
Has the SAAG replaced the transudate/exudate classification?
Yes, for determining the cause of ascites. The gradient distinguishes portal-hypertensive from non-portal causes more reliably than the older protein-based exudate/transudate concept.
Can a high SAAG and an infection coexist?
Yes. A patient with cirrhosis (high gradient) can still develop spontaneous bacterial peritonitis or another secondary process. The gradient tells you about portal pressure, not whether infection is present.
Why must both samples be from the same day?
Albumin levels shift over time, so paired samples taken on the same day give an accurate gradient. Using values from different days can produce a misleading result.
References
- Runyon BA, Montano AA, Akriviadis EA, et al. The serum-ascites albumin gradient is superior to the exudate-transudate concept in the differential diagnosis of ascites. Ann Intern Med. 1992;117(3):215–220.
- European Association for the Study of the Liver (EASL). Clinical Practice Guidelines on the management of ascites in decompensated cirrhosis.
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