The serum ascites albumin gradient (SAAG) is a medical term for the differential in albumin concentration between blood serum and ascitic fluid. Physicians utilize this disparity to distinguish between the many sources of aberrant fluid buildup, particularly portal hypertension.

Learn how to use our SAAG calculator to compute the serum-ascites albumin gradient appropriately. Meanwhile, see this related Serum Osmolality Calculator.

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What is ascites?

An accumulation of fluid in your abdomen we also know as ascites. Cirrhosis, a liver ailment, is frequently the cause. If you have cirrhosis and discover that you’re gaining weight fast, talk to your doctor. Your doctor will discuss therapies with you, which may include a low-salt diet. The stomach, intestines, pancreas, liver, spleen, and kidneys are all located in the abdomen (tummy). These organs are surrounded by a membrane of tissue called the peritoneum. There are two levels to it. The abdominal wall is lined with one layer. The organs are covered by the other.

The layers create a modest quantity of fluid to allow the abdominal organs to move freely. However, fluid can build up between the two layers, causing the abdomen to expand. This may be really inconvenient. When too much fluid builds up in your abdomen, we call it ascites (ay-SITE-EEZ) (belly). Cirrhosis (liver scarring) patients are more likely to develop this disorder. There are two layers to the peritoneum. When fluid accumulates up between the two layers, ascites develops.

About SAAG and its interpretation

The serum ascites albumin gradient (SAAG) is more accurate than total protein concentration or other measures in classifying ascites. Oncotic-hydrostatic balance is the foundation of the SAAG. The portal bed and ascitic fluid have an excessively high hydrostatic pressure gradient resulting from portal hypertension. There must be a significant difference between ascitic fluid and intravascular oncotic forces. Albumin’s oncotic force per gram is higher than that of other proteins. As a result, the difference between serum and ascitic fluid albumin concentrations is directly proportional to portal pressure.

Since the 1980s, certain laboratories have routinely measured the albumin content of the ascitic fluid. Nonetheless, before submitting ascitic fluid to a laboratory for the first time to evaluate albumin content, a physician should consult with the laboratory chemist about the procedure. Because many patients with ascites have a serum albumin concentration in the range of 2.0 g/dL (20 g/L) and an ascitic fluid albumin concentration in the range of 0 to 1.0 g/dL the accuracy of the albumin assay at low albumin concentrations (e.g., less than 1 g/dL [10 g/L]) should be confirmed. The SAAG will be artificially low if a patient with cirrhosis has a serum albumin level of less than 1.1 g/dL (11 g/L), which happens in less than 1% of individuals with cirrhotic ascites.

The SAAG’s accuracy suffers when serum and ascites specimens are not acquired almost simultaneously. The samples should be collected on the same day, ideally within an hour of each other. The amounts of albumin in serum and ascitic fluid alter throughout time, but they do so in lockstep. Thus the differential remains steady. A reduction in portal pressure and a constriction of the SAAG might occur due to arterial hypotension. Lipid can interfere with albumin assays, and chylous ascites can cause an erroneously high SAAG.

Describing the ascitic fluid

We use the AFTP measurement to identify ascitic fluid as transudate (arises as serum filtrate owing to high hydrostatic pressure or decreasing oncotic pressure of the blood) or exudate (arises as serum filtrate due to elevated hydrostatic pressure or lowered oncotic pressure of the blood) (leaks from the serum through the inflamed blood vessel walls). However, in the case of portal hypertension, this difference is less convincing. The word ascites comes from the Greek word askos, which means bag or sac. Therefore, the state of pathologic fluid collection within the abdominal cavity is referred to as ascites. Healthy males have little or no intraperitoneal fluid, but women might have up to 20 mL, depending on their menstrual cycle phase. This page focuses solely on cirrhosis-related ascites.

High gradient

With roughly 97 percent accuracy, a high gradient (>1.1 g/dL, >11 g/L) shows that the ascites is attributable to portal hypertension, either liver-related or non-liver-related. This is due to an increase in hydrostatic pressure inside the hepatic portal system’s blood capillaries, which drives water into the peritoneal cavity while leaving proteins like albumin in the vasculature.

Cirrhosis of the liver, heart failure, Budd-Chiari syndrome, portal vein thrombosis, and idiopathic portal fibrosis are all common causes of high SAAG ascites (> 1.1 g/dL, >11 g/L).

Low gradient

A low gradient (1.1 g/dL, 11 g/L) implies ascites caused by conditions other than increased portal pressure, such as TB, pancreatitis, infections, serositis, peritoneal carcinomatosis, and pulmonary infarcts.

Total<2.5Tuberculous Peritonitis, Nephrotic syndromeCirrhosis, Budd-Chiari (late)
Protein>2.5Cancer, Tuberculosis, Chylous ascites, PancreatitisRight HF, Budd-Chiari (early), veno-occlusive disease
Table for low gradient and total of proteins

How to calculate and interpret SAAG values?

We can calculate the SAAG by subtracting the ascitic fluid value from the serum value after measuring the albumin content in the serum and ascitic fluid sample. Unless there has been a laboratory error, the serum albumin concentration is always the higher value. The gradient is not a ratio but rather a subtraction. With an accuracy of about 97 percent, if the SAAG is 1.1 g/dL (11 g/L) or above, the patient is deemed to have portal hypertension. 21 Because the ascitic fluid albumin concentration cannot be larger than the ascitic fluid total protein concentration.

The patient has portal hypertension if the serum albumin minus ascitic fluid total protein gradient is 1.1 g/dL (11 g/L) or higher. The patient is unlikely to have portal hypertension if the SAAG is less than 1.1 g/dL (11 g/L). The SAAG does not explain the aetiology of ascites development or where the albumin comes from—the liver or the gut. It merely provides a clinician with an oblique but precise measure of portal pressure. Even with ascitic fluid infection, diuresis, therapeutic paracentesis, intravenous albumin infusions, and numerous types of liver disease, the test’s accuracy is high.

Our SAAG calculator uses the following formula:

SAAG = Serum Albumin – Ascitic Fluid Albumin