SAAG Calculator – Serum-Ascites Albumin Gradient

Created by Michał Szczuryk vel Szczerba, PhD candidate and Łucja Zaborowska, MD, PhD candidate
Reviewed by Bogna Szyk and Steven Wooding
Based on research by
Paré P, Talbot J, Hoefs JC. Serum-ascites albumin concentration gradient: a physiologic approach to the differential diagnosis of ascites. Gastroenterology (August 1983)
Last updated: Nov 23, 2022

Welcome to Omni's SAAG calculator. The serum-ascites albumin gradient (SAAG) is a medical value representing the albumin concentration difference between blood serum and the ascitic fluid. This discrepancy is used by physicians to differentiate the various mechanisms of abnormal fluid accumulation, especially portal hypertension.

Read along to learn how to correctly calculate the serum-ascites albumin gradient using our SAAG calculator.

If you find this article helpful, you may also like our total body water calculator or the albumin globulin ratio tool.

What is ascites?

Ascites is defined as a buildup of more than 25 mL of fluid located in the peritoneal cavity. It can arise in various mechanisms with different underlying causes. Characteristics of the ascitic fluid can be used to link the diagnosis of ascites with its true etiology.

Two main parameters are key in the assessment of the peritoneal fluid: serum-ascites albumin gradient (SAAG) and ascitic fluid total protein (AFTP). The former – the main focus of this article – is considered more useful in the identification of portal hypertension; whereas the latter remains important in the differential diagnosis of ascites.

Describing the ascitic fluid

The AFTP measurement is used to classify the ascitic fluid as transudate (arises as serum filtrate due to elevated hydrostatic pressure or lowered oncotic pressure of the blood) or exudate (leaks from the serum through the inflamed blood vessel walls). However, this distinction is less conclusive in the diagnosis of portal hypertension.

Transudate ascites can concentrate blood by removing water from the serum. Using our free water deficit calculator, you can calculate how much water is needed to counteract this process.

How to calculate and interpret SAAG values

Our SAAG calculator uses the following formula:

SAAG = serum albumin - ascitic fluid albumin

An example calculation can look like this:

SAAG = 4.23 g/dL - 3.54 g/dL = 0.69 g/dL

Because the fluids in the human body are in dynamic equilibrium, it is critical for both albumin measurements to be carried out at the same time.

Importantly, varying albumin levels during ascites affect the calculation of calcium levels. We can correct this inaccuracy can, however, with the help of our corrected calcium calculator.

  • SAAG > 1.1 g/dL (>11 g/L) is a reliable (97% accuracy) diagnostic of portal hypertension (or a non-peritoneal condition) as the cause of ascites. However, the value of ascites albumin gradient alone does not provide any clues to the cause of this hypertension (e.g., liver cirrhosis). This range corresponds to the ascitic fluid being a transudate.

  • SAAG < 1.1 g/dL (<11 g/L) indicates ascites of non-portal nature or a peritoneal origin (for example, peritonitis). This range corresponds to the exudate nature of the ascitic fluid.

Michał Szczuryk vel Szczerba, PhD candidate and Łucja Zaborowska, MD, PhD candidate
Serum albumin concentration
Ascitic fluid albumin concentration
Serum-ascites albumin gradient
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