SAAG
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Searching for SAAG (Serum-Ascites Albumin Gradient) across calculation, interpretation, and clinical utility.
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SAAG serum ascites albumin gradient calculation interpretation
Harrison's Principles of Internal Medicine, Twenty First Edition
Page 1328
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SAAG causes high low ascites differential diagnosis
Harrison's Principles of Internal Medicine, Twenty First Edition
Page 1328
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SAAG (Serum-Ascites Albumin Gradient)
Calculation
SAAG = Serum albumin − Ascitic fluid albumin
Both values must be measured on the same day. The result does not change with diuresis, making it reliable even in patients on diuretic therapy.
Interpretation
| SAAG | Pathophysiology | Clinical Meaning |
|---|---|---|
| ≥ 1.1 g/dL | Portal hypertension | Ascites driven by elevated hepatic sinusoidal pressure |
| < 1.1 g/dL | Non-portal hypertensive | Ascites from other mechanisms (exudative, inflammatory, malignant, etc.) |
The SAAG correlates with the hepatic venous pressure gradient (HVPG). Per Starling's law, the high SAAG reflects the oncotic pressure that counterbalances elevated portal pressure (Harrison's, p. 1328).
Accuracy is approximately 97% in distinguishing the two categories.
Causes by SAAG Category
SAAG ≥ 1.1 g/dL (Portal Hypertension)
- Cirrhosis (most common)
- Cardiac ascites (right heart failure, constrictive pericarditis)
- Budd-Chiari syndrome (hepatic vein thrombosis)
- Sinusoidal obstruction syndrome (veno-occlusive disease)
- Massive liver metastases
- Portal vein thrombosis
- Alcoholic hepatitis
SAAG < 1.1 g/dL (Non-Portal Hypertensive)
- Peritoneal carcinomatosis
- Peritoneal tuberculosis
- Pancreatitis (pancreatic ascites)
- Nephrotic syndrome
- Serositis (connective tissue diseases)
- Chylous ascites
- Biliary ascites
Key Clinical Points
- Spontaneous bacterial peritonitis (SBP) develops almost exclusively in portal hypertensive (high SAAG) ascites — ascitic fluid PMN ≥ 250 cells/µL is diagnostic.
- Total ascitic protein complements SAAG: in cardiac ascites, total protein is typically > 2.5 g/dL despite a high SAAG (distinguishing it from cirrhotic ascites where total protein is usually low).
- A patient can have mixed ascites (e.g., cirrhosis + peritoneal TB) — the SAAG will still be ≥ 1.1 due to the dominant portal hypertensive component, but clinical context and additional fluid studies are required.
- The test is not affected by diuresis, making it superior to the older transudate/exudate classification by Light's criteria (which was developed for pleural fluid and is unreliable for ascites).
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