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The serum-ascites albumin gradient compares albumin in a blood sample with albumin in ascitic fluid drawn on the same day. It is used to sort ascites into two broad groups: conditions driven by portal hypertension and conditions with other causes. This calculator subtracts the ascites value from the serum value and applies the widely used 1.1 g/dL threshold.
Serum-ascites albumin gradient with a 1.1 g/dL threshold.
SAAG = serum albumin − ascites albumin (g/dL)
A gradient of 1.1 g/dL or more is commonly associated with portal hypertension, while a value below 1.1 is associated with other causes of ascites. The samples should be collected close together, ideally on the same day, because albumin levels can change. The gradient indicates a category, not a specific disease.
| Symbol | Meaning |
|---|---|
| serum albumin | Albumin concentration in serum, in g/dL. |
| ascites albumin | Albumin concentration in ascitic fluid, in g/dL. |
| SAAG | The difference between the two albumin values. |
| 1.1 g/dL | Common threshold separating portal hypertensive from other ascites. |
SAAG = 3.8 − 2.4 = 1.4 g/dL. Because 1.4 is at or above 1.1, the result points toward portal hypertension as the mechanism. A second patient with serum 3.0 g/dL and ascites 2.2 g/dL has a gradient of 0.8 g/dL, which falls below the threshold and suggests a different cause. Neither result identifies the underlying disease on its own.
The serum-ascites albumin gradient is useful because it separates ascites into two mechanistic groups with a single subtraction. It works because albumin crosses the peritoneal membrane relatively slowly, so a pressure difference in the portal circulation produces a measurable concentration difference between serum and ascitic fluid. That makes the gradient a better discriminator than total protein, which is affected by other factors. It is still an indirect test. A high gradient tells you portal hypertension is likely, not why it is there; a low gradient narrows the differential but does not name the cause. Fluid cell counts, cultures, cytology and imaging usually do the rest. The arithmetic is trivial, but the interpretation belongs with the clinical picture and the laboratory results.
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Serum-ascites albumin gradient. It is the serum albumin concentration minus the ascites albumin concentration, both measured in g/dL. The gradient reflects the pressure difference across the portal circulation more closely than total protein does.
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Last reviewed: September 2026. See how we build and check every tool on the about page.
Content updated: September 2026