SAAG Calculator – Serum-Ascites Albumin Gradient

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.

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.

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, 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 a non-portal nature or a peritoneal origin (for example, peritonitis). This range corresponds to the exudate nature of the ascitic fluid.