SAAG Calculator

Ascites, the abnormal accumulation of fluid in the abdominal cavity, is a significant clinical sign that points to an underlying medical condition. One of the most critical steps in diagnosing the cause of ascites is to analyze the fluid itself. The Serum-Ascites Albumin Gradient (SAAG) calculator is a simple yet powerful tool used by healthcare professionals to help determine the underlying cause, primarily by indicating the presence or absence of portal hypertension.

What is SAAG?

SAAG is a calculation that compares the concentration of albumin (a major protein) in the blood serum to its concentration in the ascitic fluid. Albumin plays a crucial role in maintaining oncotic pressure—the pressure that helps keep fluid within the blood vessels.

The principle behind the SAAG is based on the understanding of hydrostatic and oncotic pressures. When the pressure inside the blood vessels of the liver (portal pressure) is high, it forces fluid out into the abdominal cavity. Because the vessel lining acts as a filter, this fluid is low in protein. In contrast, when ascites is caused by something other than high portal pressure (like an infection or cancer), the fluid often has a high protein content. The SAAG quantifies this difference.

The SAAG Calculation

The formula is a straightforward subtraction:

SAAG = (Serum Albumin) - (Ascitic Fluid Albumin)

To perform this calculation, a doctor takes a blood sample to measure serum albumin and performs a procedure called paracentesis to collect a sample of the ascitic fluid for analysis. Both values are typically measured in grams per deciliter (g/dL).

Interpreting the SAAG Result

The SAAG value is highly effective at differentiating between two main categories of causes for ascites. The key threshold is 1.1 g/dL.

High SAAG (≥ 1.1 g/dL)

A high gradient strongly suggests that the ascites is caused by **portal hypertension**. Portal hypertension is an increase in the pressure within the portal venous system, which drains blood from the digestive organs to the liver. This high pressure forces low-protein fluid to "leak" out of the blood vessels and into the abdomen. A high SAAG is found in over 97% of cases of portal hypertension.

Common causes of portal hypertension and high-SAAG ascites include:

• Cirrhosis of the Liver: This is the most common cause, accounting for about 85% of cases. Scarring of the liver obstructs blood flow, leading to increased portal pressure.
• Alcoholic Hepatitis: Acute inflammation of the liver from excessive alcohol use.
• Heart Failure: Particularly right-sided heart failure, which can lead to congestion of blood in the liver.
• Budd-Chiari Syndrome: A rare condition involving the blockage of the veins that drain the liver.
• Portal Vein Thrombosis: A blood clot in the portal vein.

Low SAAG (< 1.1 g/dL)

A low gradient indicates that the ascites is likely *not* caused by portal hypertension. In these cases, the mechanism for fluid accumulation is different—often due to inflammation or disease of the peritoneum (the lining of the abdominal cavity), which allows protein-rich fluid to seep into the abdomen.

Common causes of low-SAAG ascites include:

• Peritoneal Carcinomatosis: Cancer that has spread to the peritoneum.
• Tuberculosis (TB) Peritonitis: An infection of the peritoneum caused by the tuberculosis bacterium.
• Pancreatitis: Inflammation of the pancreas can cause fluid to leak into the abdominal cavity.
• Nephrotic Syndrome: A kidney disorder that causes the body to excrete too much protein in the urine, leading to very low albumin levels in the blood and generalized swelling (edema), which can include ascites.
• Serositis: Inflammation of the lining of organs, as seen in conditions like lupus.

Clinical Significance

The SAAG calculation is a crucial diagnostic step. By quickly and accurately categorizing the type of ascites, it allows clinicians to narrow down the potential underlying causes significantly. This guides the subsequent diagnostic workup and helps in formulating an appropriate treatment plan much more efficiently. For example, a patient with a high SAAG will undergo further evaluation focused on liver and heart function, while a patient with a low SAAG may need investigations to look for cancer or infection.

Disclaimer: This calculator is intended for educational purposes and for use by medical professionals. It is not a substitute for a professional medical evaluation and diagnosis. The interpretation of SAAG and the diagnosis of medical conditions should only be performed by a qualified healthcare provider.