From the Guidelines
To calculate the Serum-Ascites Albumin Gradient (SAAG), subtract the albumin concentration in the ascitic fluid from the albumin concentration in the serum, using the formula: SAAG = Serum albumin - Ascitic fluid albumin, as recommended by the most recent guidelines 1. The process requires drawing a blood sample to measure serum albumin and performing a paracentesis to obtain ascitic fluid for albumin measurement, with both measurements taken on the same day for accuracy.
- A SAAG value ≥1.1 g/dL indicates portal hypertension as the cause of ascites, such as cirrhosis, heart failure, or Budd-Chiari syndrome.
- A value <1.1 g/dL suggests non-portal hypertensive causes, like malignancy, tuberculosis, or pancreatitis. This calculation is valuable because it helps differentiate the underlying cause of ascites more accurately than the traditional transudate-exudate classification, as supported by recent studies 1. The SAAG reflects the pressure gradient between the portal venous system and the ascitic fluid, making it physiologically relevant for determining the mechanism of ascites formation, and its interpretation is summarized in Table 4 of the 2021 practice guidance by the American Association for the Study of Liver Diseases 1.
From the Research
Serum-Ascites Albumin Gradient (SAAG) Formula
The formula to calculate the Serum-Ascites Albumin Gradient (SAAG) is:
- SAAG = Serum albumin concentration - Ascitic fluid albumin concentration
SAAG Calculation and Interpretation
- The SAAG is calculated by subtracting the ascitic fluid albumin concentration from the serum albumin concentration 2, 3, 4.
- A high SAAG (≥1.1 g/dl) indicates portal hypertension, whereas a low SAAG (<1.1 g/dl) suggests no portal hypertension 2, 3, 4.
- The SAAG is a useful marker for differentiating between causes of ascites, such as cirrhosis, heart failure, and malignant ascites 2, 4.
Clinical Applications of SAAG
- The SAAG can be used to predict the presence of esophageal varices in patients with cirrhosis and ascites 3.
- The SAAG is superior to the exudate-transudate concept in classifying ascites and identifying the underlying cause 4.
- The SAAG has limited clinical implications in relation to the extent of portal hypertension in patients with liver cirrhosis 5.