SAAG Calculator

Free SAAG Calculator - Find the Cause of Ascites in Seconds

Ascites, fluid building up in the belly, can come from a long list of causes, and figuring out which one is behind a specific case used to mean sorting through the old exudate versus transudate rules that often gave confusing answers. The Serum-Ascites Albumin Gradient, or SAAG, replaced that older approach because it sorts ascites causes far more reliably, using nothing more than two albumin values from a routine blood test and a paracentesis sample.

This SAAG calculator takes your serum albumin and ascitic fluid albumin values, subtracts one from the other, and tells you instantly whether the result points toward portal hypertension or toward a cause unrelated to it. Add the ascitic fluid total protein too, and the calculator goes a step further, helping separate cirrhosis from cardiac causes within the high-gradient group.

What Is SAAG and Why Doctors Use It

SAAG stands for Serum-Ascites Albumin Gradient. It is calculated by subtracting the albumin level in the ascitic fluid from the albumin level in the blood, both measured in g/dL, on samples taken close together in time. The number that comes out reflects something simple but powerful: how much oncotic pressure difference exists between the bloodstream and the fluid sitting in the belly.

Albumin is the main protein in blood that holds water inside blood vessels through oncotic pressure. When portal pressure rises, as it does in cirrhosis or heart failure, fluid gets pushed out of the blood vessels lining the gut and liver, but albumin mostly stays behind. That mismatch shows up as a wide gap, a high SAAG. When ascites forms for a different reason, such as infection, cancer spread, or protein loss, albumin often leaks out right along with the fluid, so the gap stays small, a low SAAG.

The SAAG Formula

The math behind this calculator is a single subtraction:

• SAAG = Serum Albumin (g/dL) − Ascitic Fluid Albumin (g/dL)
• Both values should come from samples taken on the same day, ideally within hours of each other, since albumin levels can shift.
• A SAAG of 1.1 g/dL or higher indicates portal hypertension with about 97% accuracy, according to the research this cutoff is based on.
• A SAAG below 1.1 g/dL points away from portal hypertension and toward a different mechanism entirely.

How This Calculator Works

Enter your serum albumin and ascitic fluid albumin values in either g/dL or g/L, whichever unit your lab report uses, and the calculator converts automatically. It subtracts the two values, compares the result against the 1.1 g/dL cutoff, and tells you which category the result falls into, along with a plain-language explanation and a list of the conditions most associated with that category.

If you also know the ascitic fluid's total protein level, enter that too. It's optional, but within the high-gradient group it lets the calculator distinguish cirrhotic ascites from cardiac ascites, since both raise the SAAG but call for very different next steps.

Advanced Feature: Automatic Unit Conversion

Albumin is reported in g/dL in the United States and in g/L in many other countries. This calculator accepts either unit and converts automatically using the standard 10x conversion factor, so the 1.1 g/dL threshold always gets applied against the correct value, no matter which unit your lab used.

Advanced Feature: High-Gradient Sub-Classification

A high SAAG on its own only tells you portal hypertension is present, not which underlying condition is driving it. Ascitic fluid total protein helps close that gap. Cirrhotic ascites usually carries a low ascitic protein, under 2.5 g/dL, because a scarred liver struggles to push protein-rich lymph into the abdominal cavity. Cardiac ascites and Budd-Chiari syndrome usually carry a higher ascitic protein, 2.5 g/dL or above, since the congestion driving the fluid buildup sits downstream of a working liver. This calculator applies that distinction automatically whenever a total protein value is entered.

Advanced Feature: Visual Bar Chart with Reference Line

Rather than a single number, this calculator shows serum albumin, ascitic fluid albumin, and the resulting gradient side by side on a chart, with a marked reference line at the 1.1 g/dL cutoff. Seeing the gap visually makes it easier to understand how the gradient was derived and how far the result sits from the diagnostic threshold, rather than just reading a bare number off a lab slip.

Causes of High SAAG (Portal Hypertension)

A SAAG of 1.1 g/dL or above suggests the ascites is being driven by raised pressure in the portal venous system. The most common causes include:

• Cirrhosis — Accounts for roughly 80% of high-gradient ascites cases
• Alcoholic hepatitis — Liver inflammation raising portal pressure
• Heart failure (cardiac ascites) — Right-sided congestion backs pressure into the portal system
• Constrictive pericarditis — Restricts heart filling, raising venous and portal pressure
• Budd-Chiari syndrome — Hepatic vein outflow obstruction
• Portal vein thrombosis — Blocked portal flow raises upstream pressure
• Massive liver metastases — Tumor burden disrupts normal portal flow
• Fulminant hepatic failure — Acute liver failure with portal hypertension

Causes of Low SAAG (Non-Portal Hypertension)

A SAAG below 1.1 g/dL suggests a cause unrelated to portal pressure, more often tied to inflammation, infection, cancer, or protein loss. Common causes include:

• Peritoneal carcinomatosis — Cancer spread across the peritoneal lining
• Tuberculous peritonitis — TB infection of the peritoneum
• Pancreatic ascites — Leaking pancreatic fluid irritates the peritoneum
• Bowel obstruction or infarction — Fluid shifts unrelated to portal pressure
• Nephrotic syndrome — Low albumin from urinary protein loss
• Serositis (connective tissue disease) — Inflammatory fluid from lupus or similar conditions
• Biliary ascites — Bile leak into the peritoneal cavity

SAAG vs the Older Exudate-Transudate Classification

Ascitic fluid used to be classified as an exudate or a transudate based on its total protein content alone, borrowing a rule originally developed for pleural fluid. That approach performs poorly for ascites specifically, misclassifying a meaningful share of cases, particularly in people with both cirrhosis and an infection, or those on diuretics, which can raise ascitic protein even when the underlying cause is still portal hypertension.

SAAG replaced that method because it tracks the actual physiology driving fluid formation rather than just measuring protein content, and multiple studies have confirmed it performs far more reliably across a wide range of clinical situations.

Common Mistakes People Make When Interpreting SAAG

• Comparing serum and ascitic albumin drawn days apart — albumin levels can shift with hydration, illness, and treatment, so both samples should be taken close together in time.
• Assuming a high SAAG means cirrhosis specifically — a high SAAG only confirms portal hypertension as the mechanism; heart failure, Budd-Chiari syndrome, and portal vein thrombosis can all produce the same high gradient.
• Ignoring a borderline result near 1.1 g/dL — values very close to the cutoff should be interpreted alongside the full clinical picture rather than treated as a hard yes-or-no answer.
• Forgetting to convert units — mixing g/dL and g/L without converting will produce a meaningless gradient, since the two units differ by a factor of ten.
• Treating SAAG as the only test needed — cell counts, cultures, and cytology on the ascitic fluid still matter for detecting infection or malignancy, regardless of what the SAAG shows.

Who This SAAG Calculator Is Built For

This tool is meant for anyone who has had a paracentesis, or plans to, and wants a clear, evidence-based read on what their albumin results mean, as well as for students and clinicians who want a quick, accurate way to work through the calculation without doing the subtraction and threshold check by hand. It pairs well with the Cholesterol Ratio Calculator and Metabolic Syndrome Calculator on this site, since liver and metabolic health are often connected.

This calculator is built on the standard, widely validated 1.1 g/dL SAAG cutoff used in gastroenterology and hepatology practice. It's designed to help you understand what your own lab values mean, not to replace a doctor's evaluation. Ascites is always worth discussing with a physician, especially if it's new, rapidly worsening, or associated with fever, abdominal pain, or confusion.